Which one of the following is not the formula of a salt?
HCl
NaCl
MgCl_{2
(NH4)2 SO4}

Options

A. HCl
B. NaCl
C. `MgCl_(2)`
D. `(NH_(4))_(2)SO_(4)`

Answer

To determine which of the given options is not the formula of a salt, we need to understand the formation of salts. Salts are typically formed by the reaction of an acid with a base. The general reaction can be represented as:

**Acid + Base → Salt + Water**

Now, let's analyze each of the given options:

1. **HCl**: Hydrochloric acid is an acid and does not result from the neutralization of an acid and a base. Instead, it is itself an acid. Therefore, HCl is not a salt.

2. **NaCl**: Sodium chloride is formed from the reaction of sodium hydroxide (a base) and hydrochloric acid (an acid). This follows the salt formation reaction.

\[ \text{NaOH} + \text{HCl} \rightarrow \text{NaCl} + \text{H}_2\text{O} \]

3. **MgCl₂**: Magnesium chloride can be formed from the reaction of magnesium hydroxide (a base) and hydrochloric acid (an acid). This also follows the salt formation reaction.

\[ \text{Mg(OH)}_2 + \text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2\text{O} \]

4. **(NH₄)₂SO₄**: Ammonium sulfate is formed from the reaction of ammonium hydroxide (a base) and sulfuric acid (an acid). This follows the salt formation reaction as well.

\[ \text{NH}_4\text{OH} + \text{H}_2\text{SO}_4 \rightarrow (NH_4)_2SO_4 + \text{H}_2\text{O} \]

After analyzing all options, we can conclude that:

- HCl is not a salt.
- NaCl, MgCl₂, and (NH₄)₂SO₄ are all salts.

Thus, the answer to the question is:

**HCl is not the formula of a salt.**

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