${ }_{\mathrm{Z}}^{\mathrm{M}}A\left(g\right){⟶}_{\mathrm{Z}-4}^{\mathrm{M}-8}B\left(g\right)+(\alpha -\text{ particles })$

($\mathrm{\alpha }$. particles are helium nuclei, so will form He gas by trapping electrons). The radioactive disintegrations follows 1st order kinetics, starting with 1 mole of A in a 16.4 litre closed flask at 127° Pressure (atm) developed after two half lives is: (R = 0.082 litre atm/mol-K)