Which reaction will yield $CH_2 = C = CH_2$?

"The negative part of the addendum adds on to the carbon atom linked with the least number of hydrogen atoms." This statement is called:

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

Alkene can be prepared from alkyl halide by the following reagent: $R-CH_2-CH_2-X + \text{Base} \to \text{Alkene} + \text{Base-H} + X^-$

What is obtained when a mixture of ethylene,carbon monoxide,and water is heated at high temperature?

The metal used for the de-bromination reaction of $1, 2$-dibromoethane is: