Two aliphatic aldehydes $\mathbf{P}$ and $\mathbf{Q}$ react in the presence of aqueous $\mathrm{K}_2 \mathrm{CO}_3$ to give compound $\mathbf{R}$, which upon treatment with HCN provides compound $\mathbf{S}$. On acidification and heating, $\mathbf{S}$ gives the product shown below :

The compounds P and Q respectively are :

Two aliphatic aldehydes $\mathbf{P}$ and $\mathbf{Q}$ react in the presence of aqueous $\mathrm{K}_2 \mathrm{CO}_3$ to give compound $\mathbf{R}$, which upon treatment with HCN provides compound $\mathbf{S}$. On acidification and heating, $\mathbf{S}$ gives the product shown below :

The compound R is :

Two aliphatic aldehydes $\mathbf{P}$ and $\mathbf{Q}$ react in the presence of aqueous $\mathrm{K}_2 \mathrm{CO}_3$ to give compound $\mathbf{R}$, which upon treatment with HCN provides compound $\mathbf{S}$. On acidification and heating, $\mathbf{S}$ gives the product shown below :

The compound S is :

Match the reactions in Column I with appropriate options in Column II.

Column I	Column II
(A)	(P) Racemic mixture
(B)	(Q) Addition reaction
(C)	(R) Substitution reaction
(D)	(S) Coupling reaction