Question

Aqua regia is a mixture of concentrated HCl and concentrated \(HNO_3\) in the ratio of ____________ respectively.

• A. 1 : 2
• B. 2 : 1
• C. 1 : 3
• D. 3 : 1

Hint:

Remember the composition of Aqua Regia:
- 3 parts HCl (ends with 'l', looks like '3' in some mnemonics).
- 1 part HNO\(_3\) (has '3' in formula, so it takes the '1' part in ratio to balance the '3's).
This simple rule helps prevent swapping the numbers.

Answer 1

The Correct Option is D

Step 1: Recall what aqua regia is used for.
Aqua regia, literally royal water, is famous for dissolving gold and platinum, metals that resist ordinary acids on their own.
Step 2: Recall how it is mixed.
It is made by combining concentrated hydrochloric acid with concentrated nitric acid in a fixed volume ratio, three parts $HCl$ to one part $HNO_3$.
Step 3: See why this exact ratio matters.
Nitric acid oxidises the hydrochloric acid, releasing highly reactive nascent chlorine, which is what actually attacks and dissolves the noble metal into a soluble chloride complex. Having three times as much $HCl$ as $HNO_3$ keeps enough chlorine source available for this reaction to proceed effectively.
Step 4: Conclude.
The ratio of concentrated $HCl$ to concentrated $HNO_3$ in aqua regia is 3 to 1. \[ \boxed{3:1} \]