Question

A metal $M$ which is not affected by strong acids like conc. $HN{O_3}$ conc. ${H_2}S{O_4}$ and conc. solution of alkalies like $NaOH$ and $KOH$ .It forms $MC{l_3}$ , which finds use in tanning in photography. The metal $M$ is :
A. $Ag$
B. $Hg$
C. $Au$
D. $Cu$

Answer 1

A concentrated acid is known to contain a large amount of acid in a given volume; a dilute acid contains a small amount of acid in a given volume. When metals react with acid, they produce a salt and hydrogen gas. A metal in the reactivity series below hydrogen will not react with any acid because it is unreactive with the hydrogen ions in the solution.

Complete answer:
In the Periodic Table, gold is one of the least reactive elements. It never rusts or corrodes since it doesn't react with oxygen. Air, water, alkalis, and all acids have no effect on gold.
Uses of Gold
The metal is mostly used to make jewellery, glass, and various parts for technological devices.
It is used for tanning in photography.
Gold can be spun into thread and embroidered with.
A small covering of this metal is used to reflect the heat of sun rays on the windows of a huge building.
In addition to jewellery, gold is used in medicine. The tumour is treated with Au-198, a radioactive isotope of the element.
Hence, the correct option is C. $Au$ .

Note:
Gold is not dissolved in acid; instead, it is dissolved in a special mixture of acids. Aqua-regia is the name for the acid combination. It's made out of a $3:1$ blend of concentrated hydrochloric acid and concentrated nitric acid. Nitric acid causes hydrochloric acid to oxidise, releasing nascent chlorine, which combines with gold to form gold chloride. When the metal is needed, it can be extracted from the chloride.