ACS Analytical Chemistry Exam (2026/2027)
Q&A with Expert Solutions | A+ Graded
250 Questions | Comprehensive Coverage of Classical and Instrumental Techniques
Domain 1: Data Evaluation and Statistical Analysis
Q1-Q30 (6-12% of exam)
Q1: A series of five replicate measurements of a sodium chloride solution yields the
following concentrations (M): 0.1011, 0.1009, 0.1010, 0.1008, and 0.1012. Which of
the following best describes the precision of these measurements?
A. The average of 0.1010 M is close to the true value of 0.1000 M, indicating good accuracy
B. The standard deviation of 0.00016 M indicates excellent precision [CORRECT]
C. The range of 0.0004 M indicates poor precision
D. The variance of 2.56 x 10-8 indicates the measurements are imprecise
Correct Answer: B
Rationale: Precision refers to the reproducibility of individual measurements and is quantified by the standard
deviation or variance. The standard deviation of 0.00016 M is very small relative to the mean (0.1010 M), giving a
%RSD of approximately 0.16%, which indicates excellent precision. Option A describes accuracy, not precision.
Option C incorrectly interprets a narrow range as poor precision. Option D misinterprets the small variance value
as imprecision. The distinction between accuracy and precision is a foundational concept in the 2026 ACS
Analytical Chemistry exam.
Q2: A systematic error in a gravimetric analysis is most likely caused by which of the
following?
A. Weighing the crucible on different balances throughout the experiment
B. Reading the meniscus at slightly different angles for each measurement
C. Using a hygroscopic precipitate that absorbs atmospheric moisture during weighing
[CORRECT]
D. Fluctuations in room temperature affecting the balance reading
Correct Answer: C
Rationale: Systematic (determinate) errors affect accuracy by shifting all measurements in the same direction
consistently. A hygroscopic precipitate that consistently gains weight from atmospheric moisture introduces a
systematic positive error in all weighings, reducing accuracy. Options A, B, and D describe random (indeterminate)
errors because they cause measurements to scatter unpredictably, affecting precision rather than accuracy. The
ACS exam emphasizes distinguishing systematic from random errors.
Q3: For a Gaussian (normal) distribution of analytical data, approximately what
percentage of individual measurements is expected to fall within two standard
deviations of the mean?
A. 68.3%
B. 90.0%
C. 95.4% [CORRECT]
D. 99.7%
Correct Answer: C
Rationale: For a Gaussian distribution, approximately 95.4% of data points fall within plus or minus two standard
deviations of the mean. The 68.3% value corresponds to plus or minus one standard deviation, 95.4% to plus or
minus two, and 99.7% to plus or minus three standard deviations. These empirical rules are fundamental to
statistical data evaluation in analytical chemistry and are explicitly listed in the ACS exam content outline.
Q4: A 99% confidence interval for a single measurement is calculated as x plus or
minus 2.58 times sigma. If a pH meter reads 7.45 with a known standard deviation of
,0.05, what is the 99% confidence interval?
A. 7.45 plus or minus 0.050
B. 7.45 plus or minus 0.098
C. 7.45 plus or minus 0.129 [CORRECT]
D. 7.45 plus or minus 0.155
Correct Answer: C
Rationale: The 99% confidence interval for a single measurement is x plus or minus 2.58 times sigma. Substituting:
7.45 plus or minus 2.58 times 0.05 = 7.45 plus or minus 0.129, giving a range of 7.321 to 7.579. Option A uses the
standard deviation directly without the z-factor. Option B incorrectly uses 1.96 (the 95% confidence z-factor).
Option D uses 3.10. Understanding confidence intervals with correct z-factors is a key statistical skill tested on the
ACS exam.
Q5: A new spectrophotometric method for iron is validated against a standard
reference material certified at 5.00 ppm iron. Five replicates yield a mean of 4.92 ppm
with s = 0.08 ppm. Using Student's t-test at 95% confidence (t-critical = 2.776, df = 4),
is there a statistically significant difference?
A. Yes, because t-calculated = 2.24, which is less than t-critical = 2.776
B. No, because t-calculated = 2.24, which is less than t-critical = 2.776 [CORRECT]
C. Yes, because t-calculated = 4.46, which exceeds t-critical = 2.776
D. No, because t-calculated = 0.50, which is less than t-critical = 2.776
Correct Answer: B
Rationale: The t-test formula is t = (x-bar minus mu) / (s / sqrt(N)). Substituting: t = (4.92 minus 5.00) / (0.08 /
sqrt(5)) = 0..0358 = 2.24. Since 2.24 is less than t-critical = 2.776, there is no statistically significant
difference. Option A gives the correct calculation but draws the wrong conclusion. Option C computes t incorrectly.
Option D uses the wrong formula. The t-test for comparing a sample mean to a known value is a fundamental tool
in method validation per ACS standards.
Q6: In a least-squares linear regression calibration curve, the method minimizes which
of the following?
A. The sum of the absolute values of the residuals
B. The sum of the squared residuals [CORRECT]
C. The maximum residual value
D. The sum of the differences between x and y values
Correct Answer: B
Rationale: The method of least squares minimizes the sum of the squared residuals (vertical distances between
data points and the regression line). The equation is: minimize the sum of (y-i minus (mx-i plus b)) squared for all
data points i. Option A describes least absolute deviations. Option C describes the Chebyshev criterion. Option D is
not a valid method. Understanding least-squares regression is essential for constructing calibration curves in
quantitative analytical chemistry.
Q7: A calibration curve for glucose yields y = 0.0652x + 0.0031, where y is absorbance
and x is concentration in mg/dL. If an unknown sample gives A = 0.412, what is the
glucose concentration?
A. 5.18 mg/dL
B. 6.28 mg/dL [CORRECT]
C. 6.32 mg/dL
D. 26.9 mg/dL
Correct Answer: B
Rationale: Rearranging: x = (y minus 0.0031) / 0.0652 = (0.412 minus 0.0031) / 0.0652 = 0..0652 = 6.27
mg/dL, approximately 6.28 mg/dL. Option A fails to subtract the intercept. Option C subtracts the intercept from
the slope instead of from y. Option D inverts the division. Calibration curve calculations using y = mx + b are
fundamental quantitative skills in instrumental analysis.
Q8: The propagation of uncertainty for multiplication and division of measured
quantities requires the use of:
A. Absolute uncertainties summed directly
, B. Relative uncertainties squared, summed, and square-rooted [CORRECT]
C. The larger of the absolute uncertainties
D. Logarithmic differentiation of the expression
Correct Answer: B
Rationale: For multiplication and division, relative (fractional) uncertainties are used: the relative uncertainty of the
result equals the square root of the sum of the squares of the individual relative uncertainties. If z = xy, then
(delta-z/z) squared = (delta-x/x) squared + (delta-y/y) squared. Option A describes the addition/subtraction rule
using absolute uncertainties. Option C has no statistical basis. Option D is not the standard approach.
Distinguishing between the addition/subtraction and multiplication/division propagation rules is a critical ACS exam
competency.
Q9: The limit of detection (LOD) for an analytical method is best defined as:
A. The concentration giving a signal equal to 10 times the standard deviation of the blank
B. The concentration giving a signal-to-noise ratio of approximately 3:1 [CORRECT]
C. The lowest concentration on the linear portion of the calibration curve
D. The concentration at which the RSD equals 10%
Correct Answer: B
Rationale: The LOD is defined as the concentration producing a signal three times the standard deviation of the
blank (3 sigma), corresponding to a signal-to-noise ratio of 3:1. Option A describes the LOQ (10 sigma). Option C
describes the lower end of the working range. Option D is sometimes associated with LOQ. The 3 sigma LOD
definition is the IUPAC and ACS standard explicitly specified in the 2026 exam content outline.
Q10: The limit of quantitation (LOQ) is defined as the concentration giving a signal
equal to:
A. 3 sigma of the blank signal
B. 5 sigma
C. 10 sigma [CORRECT]
D. 20 sigma
Correct Answer: C
Rationale: The LOQ is defined as 10 sigma (10 times the standard deviation of the blank), corresponding to a
signal-to-noise ratio of 10:1. At this level, quantitative measurements can be made with acceptable precision (RSD
typically under 10%). The LOD (3 sigma) only indicates presence or absence. This distinction between LOD and
LOQ is fundamental in method validation per IUPAC and ACS standards.
Q11: An F-test is used to compare the variances of two data sets. If F-calculated
exceeds F-critical at 95% confidence, what conclusion can be drawn?
A. The means are significantly different
B. The precisions of the two data sets are significantly different [CORRECT]
C. The accuracy of the first method is superior
D. Both data sets have identical standard deviations
Correct Answer: B
Rationale: The F-test compares variances to determine if precisions differ significantly. If F-calculated (larger
variance / smaller variance) exceeds F-critical, the precisions are significantly different. Option A requires a t-test.
Option C confuses precision with accuracy. Option D states the null hypothesis, which is accepted only when
F-calculated is less than F-critical. The F-test is specifically for comparing variances/precisions per ACS standards.
Q12: The Q-test is used in analytical chemistry to:
A. Compare the means of two data sets
B. Determine whether an outlier should be retained or rejected from a small data set
[CORRECT]
C. Calculate the confidence interval for a population mean
D. Assess the linearity of a calibration curve
Correct Answer: B
Rationale: The Q-test (Dixon's Q-test) identifies and potentially rejects outliers in small data sets (typically N less
than 10). Q = gap / range, where gap is the difference between the suspected outlier and its nearest neighbor. If
Q-calculated exceeds Q-critical, the outlier can be rejected. Option A describes the t-test. Option C uses the
t-distribution. Option D uses correlation coefficient or residual analysis. The Q-test is explicitly listed in the ACS
, exam content outline for data evaluation.
Q13: A water sample is reported to contain 25 ppb of lead. For an aqueous solution
(density ~1.00 g/mL), this is equivalent to:
A. 25 ng/L
B. 25 ug/L [CORRECT]
C. 25 mg/L
D. 0.025 ug/mL
Correct Answer: B
Rationale: For aqueous solutions, ppb = ug/L. Therefore 25 ppb = 25 ug/L. Option A (ng/L) corresponds to ppt.
Option C (mg/L) corresponds to ppm. The conversions are: ppm = mg/L, ppb = ug/L, ppt = ng/L for aqueous
solutions. These are fundamental concentration unit equivalencies tested on the ACS exam.
Q14: A river water sample contains 3.5 ppm nitrate (NO3-, MW = 62.0 g/mol). What is
this in molarity?
A. 5.6 x 10^-5 M [CORRECT]
B. 3.5 x 10^-3 M
C. 5.6 x 10^-2 M
D. 2.2 x 10^-4 M
Correct Answer: A
Rationale: 3.5 ppm = 3.5 mg/L. Converting: (3.5 mg/L)(1 g/1000 mg)(1 mol/62.0 g) = 5.65 x 10^-5 M,
approximately 5.6 x 10^-5 M. Option B uses ppm directly as mg/L divided by molar mass without conversion.
Option C inverts the calculation. Option D uses incorrect molar mass. Unit conversion between ppm and molarity is
a core quantitative skill in analytical chemistry.
Q15: What is the %RSD for a data set with mean = 10.25 and standard deviation =
0.15?
A. 0.15%
B. 1.46% [CORRECT]
C. 1.50%
D. 15.0%
Correct Answer: B
Rationale: %RSD = (standard deviation / mean) x 100 = (0..25) x 100 = 1.46%. Option A reports the
standard deviation as percentage. Option C fails to divide by the mean. Option D inverts the ratio. The %RSD is the
most common way to express precision in analytical chemistry and is a standard ACS exam metric.
Q16: In analytical data, variance is best described as:
A. The square root of the average squared deviation from the mean
B. The average of the squared deviations from the mean [CORRECT]
C. The difference between maximum and minimum values
D. The ratio of standard deviation to mean, expressed as a percentage
Correct Answer: B
Rationale: Variance is the average of squared deviations from the mean, calculated as sum of (x-i minus x-bar)
squared divided by (N minus 1) for a sample. Option A describes standard deviation. Option C describes range.
Option D describes %RSD. Variance is used in F-tests and propagation of uncertainty calculations.
Q17: A 95% confidence interval for a single measurement is x plus or minus 1.96
sigma. A balance reads 0.2567 g with sigma = 0.0003 g. What is the 95% CI?
A. 0.2567 plus or minus 0.0003 g
B. 0.2567 plus or minus 0.0006 g [CORRECT]
C. 0.2567 plus or minus 0.0009 g
D. 0.2567 plus or minus 0.0012 g
Correct Answer: B
Rationale: 95% CI = 0.2567 plus or minus 1.96 x 0.0003 = 0.2567 plus or minus 0.000588, rounding to 0.0006 g.
Option A omits the z-factor. Option C uses z = 3.0. Option D uses z = 4.0. The z-factor of 1.96 for 95% confidence is
a fundamental statistical constant.
Q&A with Expert Solutions | A+ Graded
250 Questions | Comprehensive Coverage of Classical and Instrumental Techniques
Domain 1: Data Evaluation and Statistical Analysis
Q1-Q30 (6-12% of exam)
Q1: A series of five replicate measurements of a sodium chloride solution yields the
following concentrations (M): 0.1011, 0.1009, 0.1010, 0.1008, and 0.1012. Which of
the following best describes the precision of these measurements?
A. The average of 0.1010 M is close to the true value of 0.1000 M, indicating good accuracy
B. The standard deviation of 0.00016 M indicates excellent precision [CORRECT]
C. The range of 0.0004 M indicates poor precision
D. The variance of 2.56 x 10-8 indicates the measurements are imprecise
Correct Answer: B
Rationale: Precision refers to the reproducibility of individual measurements and is quantified by the standard
deviation or variance. The standard deviation of 0.00016 M is very small relative to the mean (0.1010 M), giving a
%RSD of approximately 0.16%, which indicates excellent precision. Option A describes accuracy, not precision.
Option C incorrectly interprets a narrow range as poor precision. Option D misinterprets the small variance value
as imprecision. The distinction between accuracy and precision is a foundational concept in the 2026 ACS
Analytical Chemistry exam.
Q2: A systematic error in a gravimetric analysis is most likely caused by which of the
following?
A. Weighing the crucible on different balances throughout the experiment
B. Reading the meniscus at slightly different angles for each measurement
C. Using a hygroscopic precipitate that absorbs atmospheric moisture during weighing
[CORRECT]
D. Fluctuations in room temperature affecting the balance reading
Correct Answer: C
Rationale: Systematic (determinate) errors affect accuracy by shifting all measurements in the same direction
consistently. A hygroscopic precipitate that consistently gains weight from atmospheric moisture introduces a
systematic positive error in all weighings, reducing accuracy. Options A, B, and D describe random (indeterminate)
errors because they cause measurements to scatter unpredictably, affecting precision rather than accuracy. The
ACS exam emphasizes distinguishing systematic from random errors.
Q3: For a Gaussian (normal) distribution of analytical data, approximately what
percentage of individual measurements is expected to fall within two standard
deviations of the mean?
A. 68.3%
B. 90.0%
C. 95.4% [CORRECT]
D. 99.7%
Correct Answer: C
Rationale: For a Gaussian distribution, approximately 95.4% of data points fall within plus or minus two standard
deviations of the mean. The 68.3% value corresponds to plus or minus one standard deviation, 95.4% to plus or
minus two, and 99.7% to plus or minus three standard deviations. These empirical rules are fundamental to
statistical data evaluation in analytical chemistry and are explicitly listed in the ACS exam content outline.
Q4: A 99% confidence interval for a single measurement is calculated as x plus or
minus 2.58 times sigma. If a pH meter reads 7.45 with a known standard deviation of
,0.05, what is the 99% confidence interval?
A. 7.45 plus or minus 0.050
B. 7.45 plus or minus 0.098
C. 7.45 plus or minus 0.129 [CORRECT]
D. 7.45 plus or minus 0.155
Correct Answer: C
Rationale: The 99% confidence interval for a single measurement is x plus or minus 2.58 times sigma. Substituting:
7.45 plus or minus 2.58 times 0.05 = 7.45 plus or minus 0.129, giving a range of 7.321 to 7.579. Option A uses the
standard deviation directly without the z-factor. Option B incorrectly uses 1.96 (the 95% confidence z-factor).
Option D uses 3.10. Understanding confidence intervals with correct z-factors is a key statistical skill tested on the
ACS exam.
Q5: A new spectrophotometric method for iron is validated against a standard
reference material certified at 5.00 ppm iron. Five replicates yield a mean of 4.92 ppm
with s = 0.08 ppm. Using Student's t-test at 95% confidence (t-critical = 2.776, df = 4),
is there a statistically significant difference?
A. Yes, because t-calculated = 2.24, which is less than t-critical = 2.776
B. No, because t-calculated = 2.24, which is less than t-critical = 2.776 [CORRECT]
C. Yes, because t-calculated = 4.46, which exceeds t-critical = 2.776
D. No, because t-calculated = 0.50, which is less than t-critical = 2.776
Correct Answer: B
Rationale: The t-test formula is t = (x-bar minus mu) / (s / sqrt(N)). Substituting: t = (4.92 minus 5.00) / (0.08 /
sqrt(5)) = 0..0358 = 2.24. Since 2.24 is less than t-critical = 2.776, there is no statistically significant
difference. Option A gives the correct calculation but draws the wrong conclusion. Option C computes t incorrectly.
Option D uses the wrong formula. The t-test for comparing a sample mean to a known value is a fundamental tool
in method validation per ACS standards.
Q6: In a least-squares linear regression calibration curve, the method minimizes which
of the following?
A. The sum of the absolute values of the residuals
B. The sum of the squared residuals [CORRECT]
C. The maximum residual value
D. The sum of the differences between x and y values
Correct Answer: B
Rationale: The method of least squares minimizes the sum of the squared residuals (vertical distances between
data points and the regression line). The equation is: minimize the sum of (y-i minus (mx-i plus b)) squared for all
data points i. Option A describes least absolute deviations. Option C describes the Chebyshev criterion. Option D is
not a valid method. Understanding least-squares regression is essential for constructing calibration curves in
quantitative analytical chemistry.
Q7: A calibration curve for glucose yields y = 0.0652x + 0.0031, where y is absorbance
and x is concentration in mg/dL. If an unknown sample gives A = 0.412, what is the
glucose concentration?
A. 5.18 mg/dL
B. 6.28 mg/dL [CORRECT]
C. 6.32 mg/dL
D. 26.9 mg/dL
Correct Answer: B
Rationale: Rearranging: x = (y minus 0.0031) / 0.0652 = (0.412 minus 0.0031) / 0.0652 = 0..0652 = 6.27
mg/dL, approximately 6.28 mg/dL. Option A fails to subtract the intercept. Option C subtracts the intercept from
the slope instead of from y. Option D inverts the division. Calibration curve calculations using y = mx + b are
fundamental quantitative skills in instrumental analysis.
Q8: The propagation of uncertainty for multiplication and division of measured
quantities requires the use of:
A. Absolute uncertainties summed directly
, B. Relative uncertainties squared, summed, and square-rooted [CORRECT]
C. The larger of the absolute uncertainties
D. Logarithmic differentiation of the expression
Correct Answer: B
Rationale: For multiplication and division, relative (fractional) uncertainties are used: the relative uncertainty of the
result equals the square root of the sum of the squares of the individual relative uncertainties. If z = xy, then
(delta-z/z) squared = (delta-x/x) squared + (delta-y/y) squared. Option A describes the addition/subtraction rule
using absolute uncertainties. Option C has no statistical basis. Option D is not the standard approach.
Distinguishing between the addition/subtraction and multiplication/division propagation rules is a critical ACS exam
competency.
Q9: The limit of detection (LOD) for an analytical method is best defined as:
A. The concentration giving a signal equal to 10 times the standard deviation of the blank
B. The concentration giving a signal-to-noise ratio of approximately 3:1 [CORRECT]
C. The lowest concentration on the linear portion of the calibration curve
D. The concentration at which the RSD equals 10%
Correct Answer: B
Rationale: The LOD is defined as the concentration producing a signal three times the standard deviation of the
blank (3 sigma), corresponding to a signal-to-noise ratio of 3:1. Option A describes the LOQ (10 sigma). Option C
describes the lower end of the working range. Option D is sometimes associated with LOQ. The 3 sigma LOD
definition is the IUPAC and ACS standard explicitly specified in the 2026 exam content outline.
Q10: The limit of quantitation (LOQ) is defined as the concentration giving a signal
equal to:
A. 3 sigma of the blank signal
B. 5 sigma
C. 10 sigma [CORRECT]
D. 20 sigma
Correct Answer: C
Rationale: The LOQ is defined as 10 sigma (10 times the standard deviation of the blank), corresponding to a
signal-to-noise ratio of 10:1. At this level, quantitative measurements can be made with acceptable precision (RSD
typically under 10%). The LOD (3 sigma) only indicates presence or absence. This distinction between LOD and
LOQ is fundamental in method validation per IUPAC and ACS standards.
Q11: An F-test is used to compare the variances of two data sets. If F-calculated
exceeds F-critical at 95% confidence, what conclusion can be drawn?
A. The means are significantly different
B. The precisions of the two data sets are significantly different [CORRECT]
C. The accuracy of the first method is superior
D. Both data sets have identical standard deviations
Correct Answer: B
Rationale: The F-test compares variances to determine if precisions differ significantly. If F-calculated (larger
variance / smaller variance) exceeds F-critical, the precisions are significantly different. Option A requires a t-test.
Option C confuses precision with accuracy. Option D states the null hypothesis, which is accepted only when
F-calculated is less than F-critical. The F-test is specifically for comparing variances/precisions per ACS standards.
Q12: The Q-test is used in analytical chemistry to:
A. Compare the means of two data sets
B. Determine whether an outlier should be retained or rejected from a small data set
[CORRECT]
C. Calculate the confidence interval for a population mean
D. Assess the linearity of a calibration curve
Correct Answer: B
Rationale: The Q-test (Dixon's Q-test) identifies and potentially rejects outliers in small data sets (typically N less
than 10). Q = gap / range, where gap is the difference between the suspected outlier and its nearest neighbor. If
Q-calculated exceeds Q-critical, the outlier can be rejected. Option A describes the t-test. Option C uses the
t-distribution. Option D uses correlation coefficient or residual analysis. The Q-test is explicitly listed in the ACS
, exam content outline for data evaluation.
Q13: A water sample is reported to contain 25 ppb of lead. For an aqueous solution
(density ~1.00 g/mL), this is equivalent to:
A. 25 ng/L
B. 25 ug/L [CORRECT]
C. 25 mg/L
D. 0.025 ug/mL
Correct Answer: B
Rationale: For aqueous solutions, ppb = ug/L. Therefore 25 ppb = 25 ug/L. Option A (ng/L) corresponds to ppt.
Option C (mg/L) corresponds to ppm. The conversions are: ppm = mg/L, ppb = ug/L, ppt = ng/L for aqueous
solutions. These are fundamental concentration unit equivalencies tested on the ACS exam.
Q14: A river water sample contains 3.5 ppm nitrate (NO3-, MW = 62.0 g/mol). What is
this in molarity?
A. 5.6 x 10^-5 M [CORRECT]
B. 3.5 x 10^-3 M
C. 5.6 x 10^-2 M
D. 2.2 x 10^-4 M
Correct Answer: A
Rationale: 3.5 ppm = 3.5 mg/L. Converting: (3.5 mg/L)(1 g/1000 mg)(1 mol/62.0 g) = 5.65 x 10^-5 M,
approximately 5.6 x 10^-5 M. Option B uses ppm directly as mg/L divided by molar mass without conversion.
Option C inverts the calculation. Option D uses incorrect molar mass. Unit conversion between ppm and molarity is
a core quantitative skill in analytical chemistry.
Q15: What is the %RSD for a data set with mean = 10.25 and standard deviation =
0.15?
A. 0.15%
B. 1.46% [CORRECT]
C. 1.50%
D. 15.0%
Correct Answer: B
Rationale: %RSD = (standard deviation / mean) x 100 = (0..25) x 100 = 1.46%. Option A reports the
standard deviation as percentage. Option C fails to divide by the mean. Option D inverts the ratio. The %RSD is the
most common way to express precision in analytical chemistry and is a standard ACS exam metric.
Q16: In analytical data, variance is best described as:
A. The square root of the average squared deviation from the mean
B. The average of the squared deviations from the mean [CORRECT]
C. The difference between maximum and minimum values
D. The ratio of standard deviation to mean, expressed as a percentage
Correct Answer: B
Rationale: Variance is the average of squared deviations from the mean, calculated as sum of (x-i minus x-bar)
squared divided by (N minus 1) for a sample. Option A describes standard deviation. Option C describes range.
Option D describes %RSD. Variance is used in F-tests and propagation of uncertainty calculations.
Q17: A 95% confidence interval for a single measurement is x plus or minus 1.96
sigma. A balance reads 0.2567 g with sigma = 0.0003 g. What is the 95% CI?
A. 0.2567 plus or minus 0.0003 g
B. 0.2567 plus or minus 0.0006 g [CORRECT]
C. 0.2567 plus or minus 0.0009 g
D. 0.2567 plus or minus 0.0012 g
Correct Answer: B
Rationale: 95% CI = 0.2567 plus or minus 1.96 x 0.0003 = 0.2567 plus or minus 0.000588, rounding to 0.0006 g.
Option A omits the z-factor. Option C uses z = 3.0. Option D uses z = 4.0. The z-factor of 1.96 for 95% confidence is
a fundamental statistical constant.
