Question

Select the statement(s) that is/are TRUE.

• A. Combustion always occurs in the vapor phase
• B. Combustion cannot occur if air is absent
• C. Flash point is the lowest temperature at which a vapor above a liquid will continue to burn once ignited
• D. The distinction between a fire and explosion is in their rate of energy release

Hint:

Remember: Flash point = ignition but not sustained; Fire point = sustained burning. Also, combustion always takes place in vapor phase.

Answer 1

The Correct Option is A

Step 1: Check option (A).
Yes — Combustion requires vapor-phase fuel and oxidizer mixing. Liquids/solids burn by first vaporizing and then combusting in vapor phase. Hence, correct.
Step 2: Check option (B).
Incorrect — Combustion can still occur with oxidizers other than air (pure oxygen, fluorine, etc.). Air is not mandatory.
Step 3: Check option (C).
Incorrect — That is the definition of fire point, not flash point. Flash point is the lowest temperature at which vapors ignite momentarily but may not sustain burning.
Step 4: Check option (D).
Correct — Fire vs explosion is distinguished by energy release rate. Explosions release energy almost instantaneously, fires release slowly.