Select correct statements out of following.

Options

A. `H_(3)PO_(4)` is conjugate acid of `HPO_(4)^(-2)`
B. `H_(2)PO_(3)^(-1)` is conjugate acid of `HPO_(3)^(-2)`
C. `H_(2)PO_(2)^(-1)` can be conjugate acid of `HPO_(2)^(-2)`
D. `H_(2)PO_(4)^(-1)` is conjugate acid of `H_(3)PO_(4)`

Explanation

To solve the question of selecting the correct statements regarding conjugate acids and bases, we will analyze each statement step by step.

### Step-by-Step Solution:

1. **Statement 1: H3PO4 is a conjugate acid of HPO4^2-**
- To determine if this statement is correct, we need to identify the conjugate acid of HPO4^2-.
- HPO4^2- can accept a proton (H+) to form H2PO4^-.
- Therefore, the conjugate acid of HPO4^2- is H2PO4^-, not H3PO4.
- **Conclusion:** This statement is **incorrect**.

2. **Statement 2: H2PO3^- is a conjugate acid of HPO3^2-**
- Here, we check if HPO3^2- can accept a proton to form a conjugate acid.
- When HPO3^2- accepts a proton (H+), it forms H2PO3^-.
- Hence, H2PO3^- is indeed the conjugate acid of HPO3^2-.
- **Conclusion:** This statement is **correct**.

3. **Statement 3: H2PO2^- can be a conjugate acid of HPO2^2-**
- We need to analyze if HPO2^2- can accept a proton.
- When HPO2^2- accepts a proton, it forms H2PO2^-.
- However, we must check if H2PO2^- can act as an acid. The structure of H2PO2^- indicates that it has no ionizable hydrogen that can donate a proton.
- Therefore, while H2PO2^- is formed, it cannot act as a conjugate acid.
- **Conclusion:** This statement is **incorrect**.

4. **Statement 4: H2PO4^- is a conjugate acid of H3PO4**
- To verify this, we check if H3PO4 can lose a proton to form H2PO4^-.
- When H3PO4 donates a proton (H+), it indeed forms H2PO4^-.
- Therefore, H2PO4^- is the conjugate base of H3PO4, not the conjugate acid.
- **Conclusion:** This statement is **incorrect**.

### Final Conclusion:
The only correct statement from the options provided is **Statement 2: H2PO3^- is a conjugate acid of HPO3^2-**.