Alkenes' reactivity with halogens at equal molar amounts

Steps:

• Ethene (C₂H₄) and propene (C₃H₆) are gases at RTP; equal volumes imply equal moles.
• Each undergoes electrophilic addition with Br₂, consuming 1 mol Br₂ per mol alkene.
• Calculate for 1 mol each: both react with 1 mol Br₂ (160 g).
• Verify other options fail due to differing atom counts, combustion products, or hydrogenation yields.

Why D is correct:

• Both alkenes add one Br₂ molecule across the double bond (Markovnikov's rule for propene, symmetric for ethene), so equal moles react with equal masses of Br₂ (molar mass 160 g/mol).

Why the others are wrong:

• A: Equal moles have 6 atoms (ethene) vs. 9 atoms (propene), so unequal total atoms.
• B: Combustion yields 2 mol CO₂ (ethene) vs. 3 mol CO₂ (propene), so unequal volumes at RTP.
• C: Hydrogenation gives 28 g ethane (from 1 mol ethene) vs. 44 g propane (from 1 mol propene), so unequal masses.

Final answer: D