10 " mL of " a sample of phenol was diluted with `H_2O `and made up to `1.0L`. 20 " mL of " this solution was treted with 40 mL brominating solution (a mixture of `KBrO_3` and KBr) in dil `H_2SO_4`. Excess of KI was added, and the liberated `I_2` required 15 " mL of " 0.1 M `Na_2S_2O_3` for complete reaction. 25 " mL of " the same brominating solution, on similar treatment required, 20 " mL of " 0.1 M `Na_2S_2O_3`. Calculate the weight of phenol per litre of the original sample.

Explanation

To solve the problem step by step, we will follow the provided information and apply stoichiometric principles.

### Step 1: Calculate the milliequivalents of the brominating solution used.

Given:
- Volume of brominating solution used = 40 mL

Using the formula for milliequivalents:
...