The number of hydrogen atom(s) attached to phosphorus atom in phosphonic acid is

Explanation

To determine the number of hydrogen atoms attached to the phosphorus atom in phosphonic acid (H₃PO₃), we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Chemical Formula**: The formula for phosphonic acid is H₃PO₃.

2. **Understand the Structure**: Phosphonic acid is also known as orthophosphorus acid. It contains phosphorus (P), oxygen (O), and hydrogen (H) atoms.

3. **Draw the Structure**: The structure of H₃PO₃ can be represented as:
- One phosphorus atom (P) at the center.
- Three hydrogen atoms (H) and three oxygen atoms (O) surrounding it.
- Specifically, two of the hydrogen atoms are part of hydroxyl groups (–OH), and one hydrogen atom is directly attached to the phosphorus atom.

4. **Count the Hydrogen Atoms**: In the structure:
- There is **one hydrogen atom** directly attached to the phosphorus atom.
- The other two hydrogen atoms are part of the hydroxyl groups (–OH).

5. **Conclusion**: Therefore, the number of hydrogen atoms attached to the phosphorus atom in phosphonic acid is **1**.

### Final Answer:
The number of hydrogen atoms attached to the phosphorus atom in phosphonic acid is **1**.

---