In phosphorus acid, If X is number of non-bonding electron pairs. Y is number of `sigma`-bonds and Z is number of `pi`-bonds. Then calculate value of ``"YxZ-X"`.

Explanation

To solve the problem, we need to analyze the structure of phosphorus acid (H₃PO₃) and determine the values of X, Y, and Z.

### Step-by-Step Solution:

1. **Identify the Structure of Phosphorus Acid (H₃PO₃)**:
- Phosphorus acid has the chemical formula H₃PO₃. The structure can be represented as follows:
- The phosphorus (P) atom is the central atom.
- It is bonded to three hydrogen (H) atoms and one oxygen (O) atom through a double bond.
- The oxygen atom that is double-bonded to phosphorus has one lone pair, while the other two oxygen atoms are single-bonded to phosphorus and each has one hydrogen atom attached.

2. **Count the Non-Bonding Electron Pairs (X)**:
- Non-bonding electron pairs are also known as lone pairs.
- In the structure of H₃PO₃:
- The double-bonded oxygen has 2 lone pairs.
- Each of the two single-bonded oxygens also has 2 lone pairs.
- Therefore, the total number of lone pairs:
- 2 (from double-bonded O) + 2 (from first single-bonded O) + 2 (from second single-bonded O) = 6 lone pairs.
- Thus, **X = 6**.

3. **Count the Sigma Bonds (Y)**:
- Sigma bonds are the first bonds formed between atoms.
- In H₃PO₃:
- There are 3 P-H bonds (sigma bonds).
- There is 1 P=O bond (the double bond consists of one sigma bond and one pi bond).
- There are 2 P-O bonds (single bonds).
- Therefore, the total number of sigma bonds:
- 3 (P-H) + 1 (P=O) + 2 (P-O) = 6 sigma bonds.
- Thus, **Y = 6**.

4. **Count the Pi Bonds (Z)**:
- Pi bonds are formed in double and triple bonds.
- In H₃PO₃:
- There is 1 double bond (P=O), which contains 1 pi bond.
- Thus, **Z = 1**.

5. **Calculate Y × Z - X**:
- Now we can substitute the values of Y, Z, and X into the expression Y × Z - X:
- Y × Z = 6 × 1 = 6
- Therefore, Y × Z - X = 6 - 6 = 0.

### Final Answer:
The value of Y × Z - X is **0**.