Page 1 of 160
NATIONAL GRID TASK 70 EXAM
PROPERTIES OF NATURAL GAS AND
ABNORMAL OPERATING CONDITION
ACTUAL TEST 2026/2027 AND STUDY
GUIDE ACCURATE QUESTIONS WITH WELL
ELABORATED ANSWERS WITH RATIONALES
(100% CORRECT VERIFIED SOLUTIONS)
LATEST UPDATED VERSION |GUARANTEE
1. What is the primary component of natural gas?
A) Propane
B) Methane
,Page 2 of 160
C) Ethane
D) Butane
✅ Answer: B) Methane
📘 Rationale: Natural gas is predominantly methane
(typically 70–90% by volume), with smaller amounts of
ethane, propane, butane, and other hydrocarbons.
2. Which property makes natural gas lighter than air?
A) High viscosity
B) Low vapor density (~0.6 relative to air)
C) High boiling point
D) Low molecular weight of methane
✅ Answer: B) Low vapor density (~0.6 relative to air)
📘 Rationale: Natural gas has a specific gravity of about 0.6
compared to air (1.0). This means it rises and dissipates quickly
if released outdoors.
,Page 3 of 160
3. At standard temperature and pressure (STP), natural gas
is in which state?
A) Solid
B) Liquid
C) Gas
D) Plasma
✅ Answer: C) Gas
📘 Rationale: Methane’s boiling point is -161.5°C (-258.7°F),
so it remains gaseous under normal atmospheric conditions.
4. Natural gas is odorless in its natural state. What
substance is added for leak detection?
A) Hydrogen sulfide
B) Mercaptan (e.g., tert-butyl mercaptan)
C) Chlorine
D) Ammonia
✅ Answer: B) Mercaptan
📘 Rationale: Mercaptans are sulfur-containing compounds
, Page 4 of 160
that give natural gas a distinctive “rotten egg” smell, allowing
leak detection by human senses.
5. The flammable range of natural gas in air is
approximately:
A) 1–5%
B) 4–14%
C) 15–25%
D) 50–70%
✅ Answer: B) 4–14%
📘 Rationale: Below 4% the mixture is too lean to ignite;
above 14% it is too rich. The optimal combustion range is
between these limits.
6. What is the autoignition temperature of methane?
A) 250°F (121°C)
B) 538°C (1000°F) approximately
C) 100°C (212°F)
D) 750°F (399°C)
NATIONAL GRID TASK 70 EXAM
PROPERTIES OF NATURAL GAS AND
ABNORMAL OPERATING CONDITION
ACTUAL TEST 2026/2027 AND STUDY
GUIDE ACCURATE QUESTIONS WITH WELL
ELABORATED ANSWERS WITH RATIONALES
(100% CORRECT VERIFIED SOLUTIONS)
LATEST UPDATED VERSION |GUARANTEE
1. What is the primary component of natural gas?
A) Propane
B) Methane
,Page 2 of 160
C) Ethane
D) Butane
✅ Answer: B) Methane
📘 Rationale: Natural gas is predominantly methane
(typically 70–90% by volume), with smaller amounts of
ethane, propane, butane, and other hydrocarbons.
2. Which property makes natural gas lighter than air?
A) High viscosity
B) Low vapor density (~0.6 relative to air)
C) High boiling point
D) Low molecular weight of methane
✅ Answer: B) Low vapor density (~0.6 relative to air)
📘 Rationale: Natural gas has a specific gravity of about 0.6
compared to air (1.0). This means it rises and dissipates quickly
if released outdoors.
,Page 3 of 160
3. At standard temperature and pressure (STP), natural gas
is in which state?
A) Solid
B) Liquid
C) Gas
D) Plasma
✅ Answer: C) Gas
📘 Rationale: Methane’s boiling point is -161.5°C (-258.7°F),
so it remains gaseous under normal atmospheric conditions.
4. Natural gas is odorless in its natural state. What
substance is added for leak detection?
A) Hydrogen sulfide
B) Mercaptan (e.g., tert-butyl mercaptan)
C) Chlorine
D) Ammonia
✅ Answer: B) Mercaptan
📘 Rationale: Mercaptans are sulfur-containing compounds
, Page 4 of 160
that give natural gas a distinctive “rotten egg” smell, allowing
leak detection by human senses.
5. The flammable range of natural gas in air is
approximately:
A) 1–5%
B) 4–14%
C) 15–25%
D) 50–70%
✅ Answer: B) 4–14%
📘 Rationale: Below 4% the mixture is too lean to ignite;
above 14% it is too rich. The optimal combustion range is
between these limits.
6. What is the autoignition temperature of methane?
A) 250°F (121°C)
B) 538°C (1000°F) approximately
C) 100°C (212°F)
D) 750°F (399°C)
