The reaction $_5B^8 \to _4Be^8 + _1e^0$ is due to

Which of the following is a radioactive element?

After the emission of one $\alpha$-particle followed by one $\beta$-particle from the atom of $_{92}X^{238}$,the number of neutrons in the atom will be

The $_{88}Ra^{226}$ is

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

If a radioactive isotope with atomic number $A$ and mass number $M$ emits an $\alpha$-particle,the atomic number and mass number of that new isotope will become: