Principles and Practice of Engineering (PE) – Environmental
Examination Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A | Instant Download
Pdf
1. A water sample has a pH of 6. What is the hydrogen ion concentration?
A. 1 × 10⁻³ M
B. 1 × 10⁻⁴ M
C. 1 × 10⁻⁶ M
D. 1 × 10⁻⁸ M
Answer: C
By definition, pH = −log[H⁺]. Therefore, [H⁺] = 10⁻⁶ M.
2. The primary purpose of coagulation in water treatment is to:
A. Kill pathogens
B. Remove dissolved salts
C. Destabilize colloidal particles
D. Remove taste and odor
Answer: C
Coagulation neutralizes particle charges, allowing aggregation during
flocculation.
3. The detention time in a sedimentation basin is:
A. Volume / Surface area
B. Flow rate / Volume
C. Volume / Flow rate
D. Surface area / Flow rate
Answer: C
Detention time equals basin volume divided by influent flow rate.
4. Biochemical Oxygen Demand (BOD₅) measures:
,A. Total oxygen in water
B. Chemical oxidizable matter
C. Oxygen used by microorganisms in 5 days
D. Nitrogen concentration
Answer: C
BOD₅ quantifies biodegradable organic matter over 5 days.
5. The ideal gas law is:
A. PV = nRT²
B. P = nRT/V²
C. PV = nRT
D. V = nR/PT
Answer: C
This equation relates pressure, volume, temperature, and moles.
6. In activated sludge systems, MLSS stands for:
A. Mean Liquid Suspended Solids
B. Maximum Loading Suspended Solids
C. Mixed Liquor Suspended Solids
D. Minimum Level Settled Solids
Answer: C
MLSS measures biomass concentration in aeration tanks.
7. Henry’s Law relates:
A. Gas pressure and volume
B. Gas solubility and partial pressure
C. Temperature and enthalpy
D. Reaction rate and concentration
Answer: B
Gas solubility in liquid is proportional to partial pressure.
, 8. The main greenhouse gas from landfills is:
A. CO₂
B. N₂O
C. SO₂
D. CH₄
Answer: D
Methane is produced during anaerobic decomposition.
9. The Reynolds number determines:
A. Temperature change
B. Pressure drop
C. Flow regime (laminar or turbulent)
D. Chemical reaction rate
Answer: C
Re < 2000 laminar; > 4000 turbulent.
10. Nitrification converts:
A. Nitrate to nitrogen gas
B. Ammonia to nitrogen gas
C. Ammonia to nitrate
D. Nitrite to ammonia
Answer: C
Two-step biological oxidation: NH₃ → NO₂⁻ → NO₃⁻.
11. The major source of indoor radon is:
A. Drinking water
B. Outdoor air
C. Soil gas infiltration
D. Building materials only
Answer: C
Radon enters from soil through foundation cracks.
Examination Questions And Correct Answers (Verified
Answers) Plus Rationales 2025/2026 Q&A | Instant Download
1. A water sample has a pH of 6. What is the hydrogen ion concentration?
A. 1 × 10⁻³ M
B. 1 × 10⁻⁴ M
C. 1 × 10⁻⁶ M
D. 1 × 10⁻⁸ M
Answer: C
By definition, pH = −log[H⁺]. Therefore, [H⁺] = 10⁻⁶ M.
2. The primary purpose of coagulation in water treatment is to:
A. Kill pathogens
B. Remove dissolved salts
C. Destabilize colloidal particles
D. Remove taste and odor
Answer: C
Coagulation neutralizes particle charges, allowing aggregation during
flocculation.
3. The detention time in a sedimentation basin is:
A. Volume / Surface area
B. Flow rate / Volume
C. Volume / Flow rate
D. Surface area / Flow rate
Answer: C
Detention time equals basin volume divided by influent flow rate.
4. Biochemical Oxygen Demand (BOD₅) measures:
,A. Total oxygen in water
B. Chemical oxidizable matter
C. Oxygen used by microorganisms in 5 days
D. Nitrogen concentration
Answer: C
BOD₅ quantifies biodegradable organic matter over 5 days.
5. The ideal gas law is:
A. PV = nRT²
B. P = nRT/V²
C. PV = nRT
D. V = nR/PT
Answer: C
This equation relates pressure, volume, temperature, and moles.
6. In activated sludge systems, MLSS stands for:
A. Mean Liquid Suspended Solids
B. Maximum Loading Suspended Solids
C. Mixed Liquor Suspended Solids
D. Minimum Level Settled Solids
Answer: C
MLSS measures biomass concentration in aeration tanks.
7. Henry’s Law relates:
A. Gas pressure and volume
B. Gas solubility and partial pressure
C. Temperature and enthalpy
D. Reaction rate and concentration
Answer: B
Gas solubility in liquid is proportional to partial pressure.
, 8. The main greenhouse gas from landfills is:
A. CO₂
B. N₂O
C. SO₂
D. CH₄
Answer: D
Methane is produced during anaerobic decomposition.
9. The Reynolds number determines:
A. Temperature change
B. Pressure drop
C. Flow regime (laminar or turbulent)
D. Chemical reaction rate
Answer: C
Re < 2000 laminar; > 4000 turbulent.
10. Nitrification converts:
A. Nitrate to nitrogen gas
B. Ammonia to nitrogen gas
C. Ammonia to nitrate
D. Nitrite to ammonia
Answer: C
Two-step biological oxidation: NH₃ → NO₂⁻ → NO₃⁻.
11. The major source of indoor radon is:
A. Drinking water
B. Outdoor air
C. Soil gas infiltration
D. Building materials only
Answer: C
Radon enters from soil through foundation cracks.
