Question

How many carbon atoms are present in one molecule of the end product?

Answer 1

When 1,3-dichloro cyclohexene reacts with alc. KOH, it undergoes elimination reaction to form cyclohex-1,3-diene.

Cyclo-1,3-diene when reacts with NBS (N-Bromo succinimide) it forms corresponding dibromo product.

This product then react with Zn, which removes both Br, to form $ZnB{r}_2$ and benzene as a product.

This benzene when reacts with $O_3$, it undergoes ozonolysis to form glyoxal ($CHO-CHO$) as a product.