Radioactive carbon dating was discovered by

The penetrating power of an $\alpha$-particle is:

An atom has a mass number of $232$ and an atomic number of $90$. How many $\alpha$-particles should it emit after the emission of two $\beta$-particles,so that the resulting atom has a mass number of $212$ and an atomic number of $82$?

Which of the following is a radioactive element?

The $\beta$-decay of $_{11}Na^{24}$ produces an isotope of

Radioactivity was discovered by