Understanding Primary Hydrogen Atoms
Primary hydrogen atoms are those that are attached to primary carbon atoms, which are connected to only one other carbon atom. To determine which compound contains only primary hydrogen atoms, we need to analyze each option.
1. Isobutene
- Isobutene (2-methylpropene) has a structure where one carbon atom is double-bonded to another carbon and has a branching, leading to some secondary hydrogen atoms.
2. 2,3-Dimethylbutene
- This compound contains double bonds and branching, resulting in hydrogen atoms attached to secondary and possibly tertiary carbons.
3. Cyclohexane
- Cyclohexane is a saturated hydrocarbon with a ring structure. Each carbon in cyclohexane is connected to two other carbons, leading to secondary hydrogen atoms.
4. Propyne
- Propyne (alkyne) has the structure HC≡C-CH3. The terminal carbon (the one with a single hydrogen) is primary, while the other carbon is involved in a triple bond, meaning it has only one hydrogen.
Conclusion
Among the options, Propyne is the only compound that contains solely primary hydrogen atoms. The terminal carbon in propyne can be classified as having only primary hydrogen, while the other carbon involved in the triple bond does not contribute to primary hydrogen count.
Thus, the answer is d) propyne.

Propyne is the correct option because in propyne only the 1 degree c atom have the hydrogen