Radioactive Decays: Alpha, Beta, Gamma question from JEE Main 2003 (AIEEE)

Answer: (a)

1. $\alpha$ and $\beta$ are material particles; $\gamma$-rays and X-rays are electromagnetic waves.
2. $\gamma$-rays come from nuclear transitions (MeV energies), X-rays from atomic transitions (keV energies).
3. Since $\lambda = \dfrac{hc}{E}$, the highest-energy photons have the least wavelength.
4. So the answer is (a) $\gamma$-rays.