Calculate the `pH` of a buffer solution containing `0.2` mole of `NH_4Cl` and `0.1` mole of `NH_4OH` per litre. `K_b` for `NH_4OH=1.85xx10^(-5)`.

Explanation

To calculate the pH of the buffer solution containing 0.2 moles of NH4Cl and 0.1 moles of NH4OH per liter, we can follow these steps:

### Step 1: Identify the components of the buffer solution
The buffer solution consists of:
- NH4Cl (which provides NH4+ ions)
- NH4OH (which is a weak base)

### Step 2: Calculate the concentration of the components
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