Which of the following gives the iodoform test?

$CH_3CH_2COCH_3 \xrightarrow{NaNO_2/HCl}$ Major product of this reaction is

$A$ compound of molecular formula $C_8H_8O_2$ reacts with acetophenone to form a single cross-aldol product in the presence of base. The same compound on reaction with conc. $NaOH$ forms benzyl alcohol as one of the products. The structure of the compound is

Predict the product $B$ in the sequence of reaction:
$HC \equiv CH$ $\xrightarrow{30\% \ H_2SO_4, HgSO_4} A$ $\xrightarrow{dil. \ NaOH} B$

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 $B$.

Identify an aldehyde used in margarine and in food for its buttery odour.