Draw a structure containing only carbon and hydrogen that is a chiral alkyne with six carbon atoms. (wedge/dash bonds are omitted for simplicity.)

The compound contains 6 Carbon atoms, its said to be an alkyne therefore compound should contain a triple bond.
There should be single C as chiral centre. This means that one carbon has 4 different groups attached to it. In the diagram shown has one carbon connected to 
1- Hydrogen 
2 - CH3 group
3 - C2H5 group
4 - C≡CH
All these groups are of different types, hence the C is a chiral centre .

Ibelieve the answer is d