Here's how to figure out the number of hydrogen atoms:

1. General Alkane Formula:

* Unbranched alkanes follow the formula C_nH_2n+2, where 'n' is the number of carbon atoms.

2. Alkene Adjustment:

* An alkene has one double bond, which means it has two fewer hydrogen atoms than the corresponding alkane.

3. Calculation:

* For a 5-carbon alkane (n=5): C₅H₂₍₅₎₊₂ = C₅H₁₂

* For a 5-carbon alkene: C₅H₁₂ - 2H = C₅H₁₀

Answer: There are 10 hydrogen atoms in an unbranched alkene with one double bond and 5 carbon atoms.