Question

Halogen acid used in the preparation of aqua regia is
A. $HF$
B. $HCl$
C. $HBr$
D. $HI$

Answer 1

Hint: To answer this question we have to know about the aqua regia. Aqua regia is a strong acid. It is prepared by mixing nitric acid and one halogen acid.

Complete Step by Step Answer:
Aqua regia is a mixture of strong nitric acid and strong hydrochloric acid. It is prepared by mixing one part of nitric acid and three parts of hydrochloric acid.
Thus the correct option is B.

Additional Information: According to Bronsted acid base theory the species which can donate its hydrogen ion is called an acid and the species or compound which can donate hydroxyl ion acts as a base. The compound which can donate hydrogen ions acts as an acid. As the hydrogen ion donating tendency of a compound increases its acidic character also increases. As we move from hydrogen fluoride to hydrogen iodide in halogen hydrides, the size of the halogen atom that is fluorine to iodine also increases. Thus the bond of the halogen atom with hydrogen atom becomes weaker and the halogen hydride can easily release the hydrogen atom and behaves as a strong acid. Thus among halogen hydrides hydrogen fluoride is the weakest and hydrogen iodide is the strongest halogen acid.
Thus we can write that $HF$ is the weakest acid.

Note: Aqua regia is widely used to remove the metals like platinum, gold etc from many compounds. It is also used to wash glass operators used in chemical labs.