Question

Alkali reacts with ammonium salts to produce corresponding salt, water and evolves ______.
A.heat
B.hydrogen
C.carbon dioxide
D.ammonia

Answer 1

Before answering this question, we should first know what alkali is. The compounds that dissolve in water to produce hydroxide ions $O{{H}^{-}}$are known as alkalis. They come in all forms. They have very complicated chemical compositions given by their chemical formulae.

Complete answer:
Alkali varies when it is about bonding: some like sodium hydroxide which is an ionic compound whereas ammonia is a simple molecule. However, they are categorized and defined by their action in the water.
Whenever ammonium salts are reacted and heated with alkalis, they release ammonia ($N{{H}_{3}}$) gas. NaOH, KOH, etc are some strong alkalis.
Some strong aqueous alkalis (bases) are-
Lithium hydroxide
Sodium hydroxide
Potassium hydroxide
Barium hydroxide
These alkalis are dissociated completely in water and give a high concentration of $O{{H}^{-}}$in the water.
Let us consider an example of sodium hydroxide (NaOH)
Ammonium chloride and sodium hydroxide reaction:
When ammonium chloride is heated with aqueous sodium hydroxide (NaOH), the product that we get is ammonia ($N{{H}_{3}}$), sodium chloride (NaCl), and water.
Aqueous ammonium chloride has weak acidic characteristics.
$N{{H}_{4}}Cl+NaOH\to N{{H}_{3}}+{{H}_{2}}O+NaCl$

So, Option (D) ammonia is correct.

Note:
Ammonium salt and alkali reaction mechanism-
Hydrogen atoms of ammonium ions have a small positive charge. Therefore, electrons of the oxygen atom in the hydroxyl ion attack that hydrogen atom. Then, one N-H bond is cleaved, and that N-H electrons go towards the nitrogen atom. It forms an ammonia molecule. Also, the cleaved hydrogen atom is taken by oxygen atoms that form a new O-H bond to produce a water molecule $({{H}_{2}}O)$.