An α - particle changes into a Helium atom. In the course of one year the volume of Helium collected from a sample of Radium was found to be 1.12×10^–2mL at STP. The number of α - particles emitted by the sample of Radium in the same time is

Ra - isotope α-emission He gas

We know that α-particles are double positively charged Helium nuclei.α-rays change to Helium gas.

Volume of He gas = 1.12$\times$10^-2 ml at STP

22400cc of the He at STP contain 6.023$\times$10²³ He-atoms

1.12$\times$10^-2 cc of He at STP contain 'X' atoms

Number of α-particles emitted = 3$\times$10¹⁷