20 mL of a solution of `H_2SO_4` neutralises 21.2 mL of 30% solution (w/v) of `Na_2CO_3`. How much water should be added to each 100 mL of the solution to bring down its strength to decinormal ?

Explanation

To solve the problem step by step, we will follow these calculations:

### Step 1: Calculate the strength of Na₂CO₃ solution
The given concentration of Na₂CO₃ is 30% w/v, which means there are 30 grams of Na₂CO₃ in 100 mL of solution.

To convert this to grams per liter:
\[
\text{Strength of Na₂CO₃} = 30 \, \text{g} \times \frac{1000 \, \text{mL}}{100 \, \text{mL}} = 300 \, \text{g/L}
...