Calculate the pH of `0.5L` of a`0.2 M NH_(4)Cl-0.2 M NH_(3)` buffer before and after addition of (a)` 0.05` mole of `NaOH` and (b) `0.05` mole of `HCl`. Assume that the volume remains constant.[Given:`pK_(a)`of `NH_(3)=4.74]`

Explanation

To solve the problem, we will calculate the pH of a buffer solution consisting of 0.2 M NH₄Cl and 0.2 M NH₃ before and after the addition of NaOH and HCl.

### Step 1: Calculate the initial pH of the buffer solution

Given:
- Concentration of NH₄Cl (salt) = 0.2 M
- Concentration of NH₃ (base) = 0.2 M
- pKₐ of NH₃ = 4.74
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