Answer:
CₙH₂ₙ
Step-by-step explanation:
Alkenes have at least one double bond between 2 of the parent chain carbons. If the general formula for alkanes (no double bonds) is CₙH₂ₙ₊₂, it makes sense that the general formula for alkenes is CₙH₂ₙ. This means that alkenes have 2 less hydrogens than their alkane counterparts.