Which one of the following gases dissolves in water to give acidic solution? A. Carbon dioxide B. Oxygen C. Nitrogen D. Hydrogen

Carbon dioxide
Oxygen
Nitrogen
Hydrogen

The correct answer is A. Carbon dioxide.

Carbon dioxide dissolves in water to form carbonic acid, which is a weak acid. The reaction is as follows:

$CO_2 + H_2O \rightleftharpoons H_2CO_3$

Carbonic acid can then dissociate into hydrogen ions and bicarbonate ions:

$H_2CO_3 \rightleftharpoons H^+ + HCO_3^-$

The hydrogen ions are what make the solution acidic.

Oxygen, nitrogen, and hydrogen do not dissolve in water to form acids.

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