Which among the following is a base?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → NaOH
A base is a substance that gives hydroxide ions (OH−) in water and neutralises an acid to form a salt and water. Sodium hydroxide dissolves as \(\ce{NaOH -> Na+ + OH-}\), so NaOH is a base (a strong one, called caustic soda).
Why the other options are incorrect
Option (1) NaCl — Incorrect. Common salt is a neutral salt, formed when NaOH neutralises HCl.
Option (3) HCl — Incorrect. Hydrochloric acid gives hydrogen ions (H+) in water, so it is an acid.
Option (4) MgCl2 — Incorrect. Magnesium chloride is a salt of magnesium hydroxide and hydrochloric acid.