Which of the following statements about hydrogen is incorrect?

Options

A. Hydrogen has three isotopes of which tritium is the most common.
B. Hydrogen never acts as cation in ionic salts.
C. Hydronium ion, `H_(3)O^(+)` exists freely in solution.
D. Dihydrogen acts as a reducing agent

Answer

To determine which statements about hydrogen are incorrect, we will analyze each option provided in the question step by step.

### Step 1: Analyzing Isotopes of Hydrogen
1. **Statement:** Hydrogen has three isotopes, out of which tritium is the most common.
- **Analysis:** Hydrogen indeed has three isotopes: protium (¹H), deuterium (²H), and tritium (³H). However, tritium is the least abundant isotope. Protium is the most common isotope of hydrogen.
- **Conclusion:** This statement is **incorrect**.

### Step 2: Analyzing Hydrogen as a Cation
2. **Statement:** Hydrogen never acts as a cation in ionic salts.
- **Analysis:** In ionic compounds, hydrogen can indeed act as a cation (H⁺). For example, in the formation of acids like HCl, hydrogen acts as a cation. Therefore, this statement is **incorrect**.
- **Conclusion:** This statement is **incorrect**.

### Step 3: Analyzing Hydronium Ion
3. **Statement:** Hydronium (H₃O⁺) exists freely in solution.
- **Analysis:** The hydronium ion (H₃O⁺) is formed when a hydrogen ion (H⁺) interacts with water (H₂O). It does exist in aqueous solutions, and it is a common representation of hydrogen ions in water.
- **Conclusion:** This statement is **correct**.

### Step 4: Analyzing Dihydrogen as a Reducing Agent
4. **Statement:** Dihydrogen acts as a reducing agent.
- **Analysis:** Dihydrogen (H₂) can act as a reducing agent in various chemical reactions, such as in the reduction of metal oxides. Therefore, this statement is **correct**.
- **Conclusion:** This statement is **correct**.

### Final Conclusion
Based on the analysis:
- The **incorrect statements** are:
- Hydrogen has three isotopes, out of which tritium is the most common.
- Hydrogen never acts as a cation in ionic salts.

### Answer:
The incorrect statements about hydrogen are:
1. Hydrogen has three isotopes, out of which tritium is the most common.
2. Hydrogen never acts as a cation in ionic salts.