`H_(3)PO_(4)hArr H^(o+) +H_(2)PO_(4)^(Theta), K_(a_(1))`:
`H_(2)PO_(4)^(Theta) hArr H^(o+) +HPO_(4)^(2-),' K_(a_(2))`:
`HPO_(4)^(2-) hArr H^(o+) + PO_(4)^(3-), K_(a_(3)):`
Mark out the incorrect statements:

Options

A. `K_(a_(1)) gt K_(a_(2)) gt K_(a_(3))`
B. `pH (H_(2)PO_(4)^(Theta)) = (pK_(a_(1))+pK_(a_(2)))/(2)`
C. Both `H_(3)PO_(4)` and `H_(2)PO_(4)^(Theta)` are more acidic than `HPO_(4)^(2-)`
D. Only `HPO_(4)^(2-)` is amphiprotic anion in the solution.

Explanation

To determine the incorrect statements regarding the ionization of phosphoric acid (H₃PO₄), we need to analyze the ionization steps and the properties of the resulting anions.

### Step-by-Step Solution:

1. **Understanding Ionization Steps**:
- The ionization of phosphoric acid occurs in three steps:
1. \( H_3PO_4 \rightleftharpoons H^+ + H_2PO_4^- \) (with ionization constant \( K_{a1} \))
2. \( H_2PO_4^- \rightleftharpoons H^+ + HPO_4^{2-} \) (with ionization constant \( K_{a2} \))
3. \( HPO_4^{2-} \rightleftharpoons H^+ + PO_4^{3-} \) (with ionization constant \( K_{a3} \))

2. **Comparing Ionization Constants**:
- Generally, for polyprotic acids like phosphoric acid, the first ionization constant (\( K_{a1} \)) is greater than the second (\( K_{a2} \)), which in turn is greater than the third (\( K_{a3} \)). This is because the first ionization produces a relatively stable anion, while subsequent ionizations produce increasingly less stable anions.
- Therefore, the statement "the value of \( K_{a1} \) is more than \( K_{a2} \) which is more than \( K_{a3} \)" is **correct**.

3. **Amphoteric Nature of Anions**:
- An amphoteric substance can act as both an acid and a base. In this case, \( H_2PO_4^- \) can accept a proton to form \( H_3PO_4 \) or donate a proton to form \( HPO_4^{2-} \). Thus, \( H_2PO_4^- \) is indeed amphoteric.
- The statement regarding the pH of \( H_2PO_4^- \) being the average of \( pK_{a1} \) and \( pK_{a2} \) is also **correct**.

4. **Acidity Comparison**:
- Since \( K_{a1} > K_{a2} > K_{a3} \), it follows that both \( H_3PO_4 \) and \( H_2PO_4^- \) are more acidic than \( HPO_4^{2-} \). Therefore, the statement "both \( H_3PO_4 \) and \( H_2PO_4^- \) are more acidic than \( HPO_4^{2-} \)" is **correct**.

5. **Identifying Amphoteric Anions**:
- The statement "only \( HPO_4^{2-} \) is an amphoteric anion in the solution" is **incorrect**. Both \( H_2PO_4^- \) and \( HPO_4^{2-} \) are amphoteric. Thus, this statement is the one that is false.

### Conclusion:
The incorrect statement is: **"Only \( HPO_4^{2-} \) is an amphoteric anion in the solution."**