What is the product formed when $trans-2$-butene reacts with $D_2$ in the presence of a $Ni$ catalyst?

The alkene $C_6H_{10}$ producing $OHC-(CH_2)_4-CHO$ on ozonolysis is

Identify the correct statements with respect to $cis/trans$-but$-2$-ene from the following:
$I$. $cis$-but$-2$-ene is more polar than $trans$-but$-2$-ene
$II$. Melting point of $cis$-but$-2$-ene is greater than that of $trans$-but$-2$-ene
$III$. Boiling point of $cis$-but$-2$-ene is greater than that of $trans$-but$-2$-ene
Correct answer is

Identify the major product $X$ in the following reaction:
$C_6H_5-CH_2-CH=CH_2 \xrightarrow{HBr, R_2O_2} X$

For the following reactions,the major products are shown: $H_2C=CH-CH=CH_2$ $\xrightarrow[0^\circ C]{HBr} CH_2=CH-CH(Br)-CH_3$ $\xrightarrow{25^\circ C} Br-CH_2-CH=CH-CH_3$. These provide an example of $1$ control at low temperature and $2$ control at higher temperature.

Which of the following compounds gives $CH_3CHO$ and $CH_3CH_2CHO$ upon ozonolysis followed by hydrolysis?