Formaldehyde can be distinguished from acetaldehyde by the use of

Match the example given in Column-$I$ with the name of the reaction in Column-$II$.

Column-$I$ (Example)	Column-$II$ (Reaction)
$(A)$ $CH_3COCl + H_2 \xrightarrow{Pd-C/BaSO_4} CH_3CHO$	$(1)$ Friedel-Crafts acylation
$(B)$ $C_6H_5CHO \xrightarrow{NaOH} C_6H_5CH_2OH + C_6H_5COONa$	$(2)$ $HVZ$ reaction
$(C)$ $C_6H_6 + CH_3COCl \xrightarrow{AlCl_3} C_6H_5COCH_3$	$(3)$ Aldol condensation
$(D)$ $R-CH_2COOH \xrightarrow{Br_2/Red P} R-CH(Br)COOH$	$(4)$ Cannizzaro's reaction
$(E)$ $CH_3-CN \xrightarrow{SnCl_2/HCl, H_2O/H^+} CH_3-CHO$	$(5)$ Rosenmund's reduction
$(F)$ $2CH_3CHO \xrightarrow{NaOH} CH_3-CH=CH-CHO$	$(6)$ Stephen's reaction

What type of reaction is the formation of aldol from aldehyde?

The starting material is $2,3-\text{dimethylbut-2-ene}$. It undergoes ozonolysis followed by reduction with $Zn/H_2O$ to form product $A$. Product $A$ then reacts with $CH_3MgBr$ followed by hydrolysis to form product $B$. Identify product $B$.

The same product $(A)$ is formed in both of the following reactions:
$1. PhMgBr + CH_3-CN \xrightarrow{H_3O^{+}} (A)$
$2. Ph-COOH \xrightarrow{(1) \text{ excess } CH_3Li, (2) H_3O^{+}} (A)$
Identify product $(A)$.

Keto-enol tautomerism is observed in which of the following?