A radioisotope `._(Z)A^(m) (t_(1//2) = 10` days) decays to give `._(z - 6)B^(m - 12)` stable atom along with `alpha`-particles. If `m g` of A are taken and kept in a sealed tube, how much He will accumulate in 20 days at `STP`.

Explanation

To solve the problem, we need to follow these steps:

### Step 1: Understand the Decay Process
The radioisotope A decays to form a stable atom B and produces alpha particles. Given that the mass number of A is m and it decays to form B with a mass number of \( m - 12 \), we can conclude that three alpha particles (each with a mass number of 4) are produced in the decay process.

### Step 2: Determine the Half-Life and Time Period
The half-life of the isotope A is given as 10 days. We need to find out how much helium will accumulate after 20 days.

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