Which of the following will form two isomers with semicarbazide?

The major product $(Y)$ in the following reactions is
$CH_3-CH(CH_3)-C\equiv CH$ $\xrightarrow[H_2O]{HgSO_4, H_2SO_4} X$ $\xrightarrow[(ii) \ conc. H_2SO_4 / \Delta]{(i) \ C_2H_5MgBr, H_2O} Y$

Toluene (excess) undergoes the following sequence of reactions:
$(i)$ $CrO_2Cl_2, CS_2$
(ii) $H_3O^+$
(iii) $NaHSO_3$
After filtration,a residue $(A)$ is obtained. This residue $(A)$ reacts with $dil. \ HCl$ to form compound $(B)$.
Identify the structures of residue $(A)$ and compound $(B)$ respectively.

Product $(D)$ in the above sequence is:

Which of the following will be dehydrated most readily in alkaline medium?

Identify the product $Y$ in the following reaction sequence:
$C_6H_6 + CH_3CH_2CH_2Cl$ $\xrightarrow{AlCl_3} X$ $\xrightarrow{KMnO_4} Y$