' x ' is the product which is obtained from benzene by reacting it...

Benzene reacts with $CO$ and $HCl$ in the presence of $CuCl$ to give benzaldehyde ($x$) via the Gattermann-Koch reaction.

Benzene reacts with ethanoyl chloride ($CH_3COCl$) in the presence of anhydrous $AlCl_3$ to give acetophenone ($y$) via Friedel-Crafts acylation.

Heating benzaldehyde ($x$) and acetophenone ($y$) in the presence of alkali results in a crossed aldol condensation to form benzalacetophenone ($z$).

$C_6H_5CHO + CH_3COC_6H_5 \xrightarrow{OH^-, \Delta} C_6H_5-CH=CH-CO-C_6H_5 + H_2O$

The structure of $z$ ($C_6H_5-CH=CH-CO-C_6H_5$) contains two phenyl rings ($6$ $\pi$ bonds), one $C=C$ double bond ($1$ $\pi$ bond), and one $C=O$ double bond ($1$ $\pi$ bond).

Total number of $\pi$ bonds = $6 + 1 + 1 = 8$

Total number of $\pi$ electrons = $8 \times 2 = 16$

Answer: $16$