Radium disintegrates at an average rate of `2.24 xx 10^13` `alpha`-particles per minute. Each a-particle takes up two electrons from the air and becomes a neutral helium atom. After 420 days, helium gas collected was 0.5 rnL, measured at 27°C and 750 mmHg. Calculate the Avogadro constant.

Answer

`6.7 xx 10^(23)`