Question

Which of the following is a strong alkali?
(A) Sodium chloride
(B) Sodium hydroxide
(C) Ammonium chloride
(D) Ammonium hydroxide

Answer 1

Hint: Out of the given options, caustic soda or lye is a strong alkali. At room temperature, it is a white, odourless solid.

Complete Solution :
Strong alkalis fully dissociate in water. Strong alkalis produce lots of hydroxide ions in solution, making the solution more basic. Few hydroxide ions are produced by weak bases making its solution less basic.
Let us see each of the given options.
- Option A is sodium chloride. It is formed from the neutralization of HCl by NaOH. It is neither acidic nor basic.
- The next option given is Sodium hydroxide. It completely dissociates in solution and forms sodium ions and hydroxide ions.
$NaOH\to N{a}^{+}+O{H}^{-}$

The more hydroxide ions you have in the solution, the larger the base dissociation constant ($K_b$) and stronger is the base. Thus, it is a strong alkali.
 Now let us check if there is any other stronger alkali present in option c and d.
- Option C- Ammonium chloride is a neutral salt but ammonium chloride solution is slightly acidic. So this is not the right option.
 - Option D - Ammonium hydroxide is a solution of ammonia and water. When ammonia is dissolved in water, the water molecules donate a proton to the ammonia molecule which results in the production of an ammonium cation. This is not the correct option, as ammonia is a weak base when compared to sodium hydroxide.
So, the correct answer is “Option B”.

Note: It is important to understand that an alkali is a compound that accepts incoming electrons or protons. Do not get confused with sodium chloride and sodium hydroxide. Sodium chloride cannot accept protons however sodium hydroxide can.