Question

Name a gas whose solution in water is alkaline.
A.Ammonia
B.Chlorine
C.$S{O_2}$
D.$HCl$

Answer 1

Hint: Alkaline refers to that part of the pH scale where the pH is greater than 7 and the solution shows the properties of alkali. In pH scale, the range is from 0 to 14 where less than 7 shows acidic nature, 7 is neutral and greater than 7 is alkaline or basic.

Complete step by step answer:
A.Ammonia
Ammonia is a compound of nitrogen and hydrogen with the formula $N{H_3}$.
Ammonia is a colourless gas with a characteristically pungent smell. It is lighter than air, its density being 0.589 times that of air.
Ammonia dissolves in water with the liberation of heat. These aqueous solutions of ammonia are basic and it is known ammonium hydroxide.
$N{H_3} + {H_2}O \rightleftharpoons N{H_4}^ + + O{H^ - }$
Water is donating ${H^ + }$ ions and a lone pair of nitrogen is accepting to form ammonium ions. The pH of ammonium hydroxide is 11.63.
Thus ammonia reacts with water to form alkaline.
B.Chlorine
Chlorine gas ($C{l_2}$) is added to the water (${H_2}O$), it hydrolyzes to produce hypochlorous acid (HOCl) and hydrochloric acid.
$C{l_2} + {H_2}O \to HOCl + HCl$
In the presence of sunlight, the chloric acid slowly decomposes to hydrochloric acid and reduces ${O_2}$ oxygen gas.
$2C{l_2} + 2{H_2}O \to 4HCl + {O_2}$
In this pH range of hypochlorous acid is 3 to 6.
Thus chlorine reacts with water; it doesn’t form alkaline because its pH is less than 7.
C.$S{O_2}$ (Sulphur dioxide)
Sulphur dioxide can dissolve in water to form Sulphurous acid (${H_2}S{O_3}$). Sulphurous acid is weakly dibasic acid.
$S{O_{2(g)}} + {H_2}O \to {H_2}S{O_{3(aq)}}$
Sulphur acid is a solution to dissolve Sulphur dioxide in equilibrium ${H^ + }$ and $HS{O_3}$ ions.
$S{O_2} + {H_2}O \rightleftharpoons {H^ + } + HS{O_3}^ - $
The pH range of sulphurous acid is 5.1.
When Sulphur dioxide reacts with water it forms sulphurous acid and it is not alkaline due to its pH being less than 7.
D.$HCl$ (Hydrogen chloride)
Hydrochloric acid is added to a water molecule to form a hydronium cation, ${H_3}{O^ + }$.
Hydrochloric acid, $HCl$, is a strong acid, right from the start to ionize completely in aqueous solution.
$HC{l_{(aq)}} + {H_2}{O_{(l)}} \to {H_3}{O^ + }_{(aq)} + C{l^ - }_{(aq)}$
Hydrochloric acid ionization will also produce chloride anions, $C{l^ - }$.
The pH range of hydrochloric acid is 5.66.
Hydrochloric acid reacts with a water molecule to form hydronium cation and it is not alkaline due to its pH being less than 7.
The $HCl$ is not gas, it is liquid.
Thus the correct answer is (A).

Note:
-Because of the alkaline characteristics of ammonium hydroxide, it is used in many industries as a surface cleaner.
-It is also used in household works and is also used as a sanitizer.