Consider two covalent compounds `AL_(n_(1)) and BL_(n_(2))`, if central atom (A) of first compounds has total six electron pairs and central atom (B) of second compound contains total five electron pairs in its valence shell and both compounds are planar and non-polar then calculate value of experssion `(n_(1)-n_(2))^(2)`.
[Where `n_(1) and n_(2)` are number of monovalent surrounding atom (L)]

Explanation

To solve the problem, we need to analyze the two compounds \( AL_{n_1} \) and \( BL_{n_2} \) based on the information provided about their central atoms and electron pairs.

### Step-by-Step Solution:

1. **Identify the Electron Pair Geometry of Compound \( AL_{n_1} \)**:
- The central atom \( A \) has a total of 6 electron pairs.
- According to VSEPR theory, 6 electron pairs correspond to an octahedral geometry.
- However, since the compound is stated to be planar and non-polar, we can deduce that it must have 4 surrounding atoms (L) and 2 lone pairs. This leads to a square planar shape.

2. **Determine the Value of \( n_1 \)**:
- In the square planar arrangement, there are 4 surrounding monovalent atoms (L).
- Therefore, \( n_1 = 4 \).

3. **Identify the Electron Pair Geometry of Compound \( BL_{n_2} \)**:
- The central atom \( B \) has a total of 5 electron pairs.
- This corresponds to a trigonal bipyramidal geometry.
- To maintain planarity and non-polarity, we can remove 3 ligands from the equatorial positions, resulting in a linear shape with 2 surrounding atoms.

4. **Determine the Value of \( n_2 \)**:
- In the linear arrangement, there are 2 surrounding monovalent atoms (L).
- Therefore, \( n_2 = 2 \).

5. **Calculate the Expression \( (n_1 - n_2)^2 \)**:
- Substitute the values of \( n_1 \) and \( n_2 \) into the expression:
\[ (n_1 - n_2)^2 = (4 - 2)^2 = 2^2 = 4 \]

### Final Answer:
The value of the expression \( (n_1 - n_2)^2 \) is **4**.