IGCSE Edexcel Chemistry Practice Test

Propene is an alkene, which are hydrocarbons with a carbon–carbon double bond. For alkenes, the general formula is CnH2n. With three carbon atoms (n = 3), you get C3H6. This matches the structure of propene, which has two fewer hydrogens than the saturated alkane with the same number of carbons (propane, C3H8) because of the double bond. The other options don’t fit: C3H8 is propane, a saturated alkane; C4H8 would be a four-carbon alkene (butene); C2H4 is ethene, with only two carbons. So the molecular formula is C3H6.