The half-life period of element $X$ is same as the mean life time of element $Y$. Assume initially $X$ and $Y$ have same number of atoms. Then

Heavy water is used as moderator in nuclear reactor because

The radius of a nucleus of mass number 27 is $R$. Which of the following is true about a nucleus whose radius is $2 R$ ?

The nucleus ${ }_{50}^{120} X$ undergoes the series of reactions given below:

$$ { }_Z^A X \xrightarrow{\alpha \text {-decay }} P \xrightarrow{\beta^{-} \text {-decay }} Q \xrightarrow{\alpha \text {-decay }} R $$

The number of neutrons in the nucleus $R$ is