Which type of bond exists between the two carbon atoms of an alkene?

In the following reaction,$A$ and $B$ respectively are
$A \xrightarrow{HBr} C_2H_5Br \xrightarrow{B} A$

Explain the dehalogenation of vicinal dihalides with an example.

$R_f$ value for $2$-methylpropene in a solvent system (Ethyl acetate + ether) is $0.42$. $2$-methylpropene is treated with dilute $H_2SO_4$ to give major organic product $(X)$. $R_f$ value for $(X)$ in the same solvent system under identical condition will be:

The products $Q$ and $R$ in the following reactions respectively are:
$H_2 + CH_3-C \equiv CH$ $\xrightarrow{\text{Lindlar's catalyst}} P$ $\xrightarrow[Zn + H_2O]{O_3} Q + R$

Addition of $BH_3$ followed by $H_2O_2$ to $trans-2-butene$ would give a product which is