Final answer:
Hydrochloric acid (HCl) is the strong acid among the substances listed, as it is known to completely ionize in water.
option(1).
Step-by-step explanation:
To identify the strong acid among the given substances, we should recall that strong acids are those that completely ionize or dissociate in water. The provided examples are:
- Hydrochloric acid (HCl)
- Milk of magnesia (Mg(OH)2)
- Soap water
Hydrochloric acid (HCl) is recognized as a strong acid because it ionizes completely when dissolved in water. On the other hand, milk of magnesia, which is magnesium hydroxide, Mg(OH)2, is a base and not an acid at all. Similarly, soap water is basic in nature and not an acid. Therefore, the correct answer to the question is that hydrochloric acid is the strong acid.