Determine C5H10 formula and count alkene isomers Steps:

• Molar volume at room conditions is 24 dm³/mol; moles of 10 g Y = 3.4 / 24 = 0.1417 mol; molar mass = 10 / 0.1417 ≈ 70 g/mol, so Y is C5H10.
• Decolorizes Br2, confirming unsaturation (alkene); excludes saturated hydrocarbons like cyclopentane.
• Acyclic alkene structural isomers: 1-pentene, 2-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 2-methyl-2-butene.
• Include stereoisomers: 2-pentene has E and Z forms; total 6 isomers.

Why C is correct:

• C5H10 alkenes have 5 structural isomers, with 2-pentene adding 2 stereoisomers for 6 total, per IUPAC nomenclature.

Why the others are wrong:

• A: Counts only 4 structural isomers, ignoring stereoisomerism.
• B: Counts 5, omitting one stereoisomer of 2-pentene.
• D: Counts 7, including saturated cyclopentane that does not decolorize Br2.

Final answer: C