One mole of A present in a closed vessel undergoes decays as:
`._(Z)A^(m) rarr ._(Z - 4)B^(m - 8) + 2 (._(2)He^(4))`
What will be the volume of helium gas collocted at `STP` afterd 20 days `(t_(1//2) "of" A = 10` days)?

Explanation

To solve the problem, we will follow these steps:

### Step 1: Determine the decay of substance A after 20 days
Given that the half-life (t₁/₂) of A is 10 days, we can calculate how much of A remains after 20 days.

- After the first 10 days (1 half-life), the amount of A will be:
\[
\text{Remaining A} = \frac{1}{2} \text{ mole}
...