The final product is cyclohexyl isocyanide ( ).

Working backwards from the final product:
The last step involves and KOH (alc), which is the Carbylamine reaction.
This reaction converts a primary amine ( ) into an isocyanide ( ). Thus, the intermediate before this step must be cyclohexylamine ( ).

The step before cyclohexylamine involves and , which is the Hoffmann Bromamide Degradation reaction.

This reaction converts an amide ( ) into a primary amine ( ) with one less carbon atom.

Therefore, the amide ' Q ' must be cyclohexanecarboxamide ( ).
The first step converts ' P ' into ' Q ' using and heat.
Carboxylic acids react with followed by heating to form amides.
Thus, ' P ' must be cyclohexanecarboxylic acid ( ).
Reaction sequence:

(Cyclohexylamine)

(Cyclohexyl isocyanide)
Comparing with the options, ' P ' is cyclohexanecarboxylic acid, which corresponds to option .