Formulae for Nessler's reagent is :

Given below are two statements: One is labelled as Assertion A and the other is labelled as Reason R.

Assertion A: can be easily reduced using $\mathrm{Zn}-\mathrm{Hg} / \mathrm{HCl}$ to

Reason $\mathrm{R}: \mathrm{Zn}-\mathrm{Hg} / \mathrm{HCl}$ is used to reduce carbonyl group to $-\mathrm{CH}_{2}-$ group.

In the light of the above statements, choose the correct answer from the options given below:

The water quality of a pond was analyzed and its BOD was found to be 4. The pond has :

The most stable carbocation for the following is: