Which of the following radiations will have maximum penetration power?

The correct answer is Option (4) → \( \gamma \)-rays

Penetrating power depends on how strongly a radiation interacts with matter: the more ionisation it causes along its path, the sooner it loses its energy. An \( \alpha \) particle is heavy and doubly charged, so it ionises strongly and is stopped by a sheet of paper. A \( \beta \) particle is light and singly charged; it ionises less and passes through a few millimetres of aluminium. X-rays and \( \gamma \)-rays are electromagnetic waves with no charge, so they ionise only weakly and go much further.

\( \gamma \)-rays come from the nucleus and have the highest photon energies (shortest wavelengths), higher than those of X-rays, so they penetrate the most and need thick lead or concrete to stop them.

    \( \alpha \lt \beta \lt \text{X-rays} \lt \gamma \quad (\text{increasing penetrating power}) \)