Select the correct statement out of following :

Alkaline solution of ${\mathrm{K}}_2{\mathrm{HgI}}_4$is known as Nessler's reagent.

Nessler's reagent is the name given to an alkaline solution of ${\mathrm{K}}_2{\mathrm{HgI}}_4$ in honour of Julius Neßler (Nessler). In the addition of ammonia, this light solution darkens to a darker yellow colour. When concentrations are greater, a brown precipitate might occur.

Hence the correct option is D.