Which of the following statements about hydrogen is incorrect ?

Options

A. Dithydrogen does not act as a reducing agent
B. Hydrogen has three isotopes of which tritium is the most common
C. Hydrogen never acts as cation in ionic salts
D. Hydronium ion, `H_(3)O^(+)` exists freely in solution

Answer

To determine which statement about hydrogen is incorrect, we will analyze each of the provided statements step by step.

### Step 1: Analyze Statement 1
**Statement 1:** Dihydrogen does not act as a reducing agent.

- **Analysis:** Dihydrogen (H₂) can react with oxygen to form water (H₂O). In this reaction, hydrogen is oxidized (its oxidation state changes from 0 in H₂ to +1 in H₂O), while oxygen is reduced (its oxidation state changes from 0 in O₂ to -2 in H₂O). Since hydrogen is causing the reduction of oxygen, it acts as a reducing agent.

**Conclusion:** This statement is incorrect.

### Step 2: Analyze Statement 2
**Statement 2:** Hydrogen has three isotopes of which tritium is the most common.

- **Analysis:** The three isotopes of hydrogen are:
1. Protium (¹H) - 99.96% abundance
2. Deuterium (²H) - 0.0156% abundance
3. Tritium (³H) - approximately 10^-15% abundance

Protium is the most common isotope, not tritium.

**Conclusion:** This statement is also incorrect.

### Step 3: Analyze Statement 3
**Statement 3:** Hydrogen never acts as cationic in ionic salts.

- **Analysis:** In ionic compounds, hydrogen typically carries a -1 charge (as in sodium hydride, NaH). It does not exist as a cation (positive charge) in these compounds; instead, it is found in anionic form.

**Conclusion:** This statement is correct.

### Step 4: Analyze Statement 4
**Statement 4:** Hydronium ion (H₃O⁺) exists freely in solution.

- **Analysis:** When an acid like HCl is dissolved in water, it dissociates to form H⁺ ions, which associate with water molecules to form hydronium ions (H₃O⁺). Therefore, hydronium ions do exist in aqueous solutions.

**Conclusion:** This statement is correct.

### Final Conclusion
The incorrect statements are:
- Statement 1: Dihydrogen does not act as a reducing agent.
- Statement 2: Hydrogen has three isotopes of which tritium is the most common.

### Summary of Incorrect Statements
- **Incorrect Statement 1:** Dihydrogen does not act as a reducing agent.
- **Incorrect Statement 2:** Tritium is the most common isotope of hydrogen.