Q. 10 mL of gaseous hydrocarbon on combustion gives 40 mL of CO₂(g) and 50 mL of water vapour. Total number of carbon and hydrogen atoms in the hydrocarbon is _____

Atoms in Hydrocarbon from Combustion Data | JEE Mains PYQ | Mole Concept

Q. 10 mL of gaseous hydrocarbon on combustion gives 40 mL of CO₂(g) and 50 mL of water vapour. Total number of carbon and hydrogen atoms in the hydrocarbon is ______ .

Explanation

Step 1: Assume hydrocarbon formula

Let the hydrocarbon be C_xH_y.

Step 2: Use volume ratios (Avogadro’s law)

10 mL hydrocarbon → 40 mL CO₂
⇒ x = 40 ÷ 10 = 4

Step 3: Use water vapour data

10 mL hydrocarbon → 50 mL H₂O
1 mole hydrocarbon produces y/2 moles of H₂O

y/2 = 50 ÷ 10 = 5
⇒ y = 10

Step 4: Calculate total atoms

Total atoms = x + y = 4 + 10 = 14

Correct Answer = 14

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