Vicinal and geminal dihalides can be distinguished by using:

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:

Ethyl orthoformate is formed by heating which of the following compounds with sodium ethoxide?

The reaction of methyl bromide with aqueous sodium hydroxide involves:

When $AgNO_3$ comes in contact with skin,it leaves a black stain. This is because of

$2-$Methylpropyl bromide reacts with $C_2H_5O^-$ to give $A$,whereas on reaction with $C_2H_5OH$ it gives $B$. The mechanism followed in these reactions and the products $A$ and $B$ respectively are: