Here's how to determine the number of hydrogen atoms in a cycloalkene with one double bond and 3 carbon atoms:

1. General Formula for Cycloalkanes:

The general formula for cycloalkanes is CₙH₂ₙ, where 'n' is the number of carbon atoms.

2. Adjusting for the Double Bond:

A double bond reduces the number of hydrogen atoms by two.

3. Applying the Formula:

* We have 3 carbon atoms (n = 3).

* The general formula for cycloalkanes with 3 carbons would be C₃H₆.

* The double bond reduces this by two, leaving us with C₃H₄.

Therefore, there are 4 hydrogen atoms in a cycloalkene with one double bond and 3 carbon atoms.