In a nucleophilic substitution reaction,the order of halogens as incoming (attacking) nucleophiles is: $I^{-} > Br^{-} > Cl^{-}$. The order of halogens as departing (leaving) nucleophiles should be:

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : Haloalkanes react with $KCN$ to form alkyl cyanides as a main product while with $AgCN$ they form isocyanide as the main product.
Reason $(R)$ : $KCN$ and $AgCN$ both are highly ionic compounds.
In the light of the above statement,choose the most appropriate answer from the options given below:

Increasing the concentration of a nucleophile in a typical $S_N2$ reaction by a factor of $10$ will cause the reaction rate to

The following bimolecular elimination reaction $(E_2)$ is carried out with different halogen leaving groups. The per cent yield of the two products ($2$-hexene and $1$-hexene) for each leaving group is listed below.

Leaving group	Conj. Acid $pK_a$	$\%$-yield of $2$-hexene	$\%$-yield of $1$-hexene
$X = I$	$-10$	$81\%$	$19\%$
$X = Br$	$-9$	$72\%$	$28\%$
$X = Cl$	$-7$	$67\%$	$33\%$
$X = F$	$3.2$	$30\%$	$70\%$

Which of the following statement$(s)$ is/are true concerning this series of $E_2$ reactions?

The major products $X$ and $Y$ respectively from the following reactions are:

The reaction of $t-$butyl bromide with sodium methoxide mainly gives .............