1. General Alkane Formula:

* An unbranched alkane with 4 carbons has the formula C₄H₁₀ (general formula: CₙH₂ₙ₊₂).

2. Double Bond Adjustment:

* A double bond replaces two hydrogen atoms. So, we subtract two hydrogens from the alkane formula: C₄H₁₀ - 2H = C₄H₈

Answer: An unbranched alkene with one double bond and 4 carbon atoms has 8 hydrogen atoms.