Which of the following reactions occurs easily in ethylene?

$CH_3-CH(CH_3)-CH=CH_2 + HBr \rightarrow A$. $A$ (predominantly) is:

The addition of $HBr$ to $2-$pentene gives

What is the major product expected from the following reaction?

The Diels-Alder reaction will not take place with which of the following reactants?

An alkene $X$ with formula $C_4H_8$ does not exhibit geometrical isomerism. In the conversion of $X$ to $Y$,the correct sequence of reagents $A$ and $B$ used are ($Y$ gives iodoform test):
$X$ $\xrightarrow{A} \text{Intermediate}$ $\xrightarrow{B} Y$