Which one of the following compounds is the best choice for being prepared by an efficient mixed aldol addition reaction?

Formalin is the commercial name of

What is the major product of the following reaction?

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.

The reaction involving the reduction of a ketone to an alkane using zinc amalgam $(Zn-Hg)$ and concentrated hydrochloric acid $(HCl)$ is known as:

What is the product $R$ in the following reaction sequence?