Acid radicals are present in

1. Analyze the question

The question asks you to identify which group of ions consists entirely of acid radicals. An acid radical is the negative ion (anion) that remains when an acid loses its hydrogen ions ($H^+$).

2. Explain the concept

• Acid Radicals: These are negatively charged ions derived from acids. For example, when Sulfuric acid ($H_2SO_4$) loses its hydrogen ions, it forms the sulfate radical ($SO_4^{2-}$).
• Basic Radicals: These are positively charged ions (cations), usually metals or the ammonium ion ($NH_4^+$).
• Key Rule: To identify the correct option, look for the set that contains only anions (negative ions). Any option containing a metal cation (like $Mg^{2+}$, $Na^+$, or $K^+$) is incorrect because those are basic radicals.

3. Show the solution

Let's evaluate each option:

• Option A: $CO_3^{2-}$ (Anion), $PO_4^{3-}$ (Anion), $Mg^{2+}$ (Cation). Since $Mg^{2+}$ is a basic radical, this is incorrect.
• Option B: $CO_3^{2-}$ (Anion), $SO_4^{2-}$ (Anion), $Na^+$ (Cation). Since $Na^+$ is a basic radical, this is incorrect.
• Option C: $CO_3^{2-}$ (Carbonate), $SO_4^{2-}$ (Sulfate), $NO_3^-$ (Nitrate). All three are negatively charged anions derived from carbonic acid, sulfuric acid, and nitric acid respectively. This fits the definition perfectly.
• Option D: $CO_3^{2-}$ (Anion), $SO_4^{2-}$ (Anion), $K^+$ (Cation). Since $K^+$ is a basic radical, this is incorrect.

4. Identify the answer

The correct option is C.

5. Tip for your exam

Remember the "Cation/Anion" split:

• Cations are Connected to the Cathode (Positive ions).
• Anions are Attracted to the Anode (Negative ions). In salt chemistry, the metal part is always the basic radical (cation), and the non-metal part (or polyatomic group) is the acid radical (anion). If you see a metal symbol like Na, K, Mg, or Ca, it cannot be an acid radical!