Steam burn is more severe than that of boiling water because

Analyze the question: Both steam and boiling water are at 100°C, yet steam causes a more severe burn. We need the reason.

Explain the concept: When water boils, it needs extra energy to change from liquid to gas without any rise in temperature. This is the latent heat of vaporization. For water, it is about 2.26 × 10⁶ J/kg (2260 J/g).

When steam touches your skin, it condenses back into water and releases this latent heat onto the skin. Only after that does the resulting 100°C water cool further and release more heat.

Solution:

Compare 1 g of each, cooling to skin temperature (about 30°C):

• Boiling water at 100°C: Q = mcΔθ = 1 × 4.2 × 70 ≈ 294 J
• Steam at 100°C: Q = mL + mcΔθ = 2260 + 294 ≈ 2554 J

So steam delivers almost 9 times more heat energy per gram than boiling water at the same temperature. That is why the burn is more severe.

Checking the options:

• A. Relative humidity is not the reason. Wrong.
• B. Steam has greater heat energy per unit mass because of latent heat. Correct.
• C. Water boils at 100°C (at normal pressure); it doesn't matter here, and the statement doesn't explain the difference. Wrong.
• D. Humidity dependence is not the reason either. Wrong.

Answer: B

Exam tip: Whenever you see "steam vs boiling water," think latent heat. Same temperature, but steam carries the extra hidden energy that is released on condensation.