An alkyne has the molecular formula $\mathrm{C}_6 \mathrm{H}_{10}$. The number of 1-alkyne isomers (excluding stereoisomers) possible for it is

• A

  $2$
• B

  $5$
• C

  $3$
• Correct answer
  D

  $4$

Hence, the correct answer is option: 'D'.