Compound $X$ on reaction with ${\text{O}}_3$ followed by ${\text{Zn/H}}_2\text{O}$ gives formaldehyde and 2-methyl propanal as products. The compound $X$ is:

1. A
   3 - Methylbut - 1 - ene
2. B
   2 - Methylbut - 1 - ene
3. C
   2 - Methylbut - 2 - ene
4. D
   Pent - 2 - ene