Radiation identification via range and electric deflection

Steps:

• Recall alpha radiation consists of positively charged helium nuclei with low penetration.
• Note the given range of a few millimeters in air matches alpha's limited travel distance due to high ionization.
• Observe deflection by electric field indicates charged particles; alpha's positive charge causes attraction to negative plate.
• Rule out uncharged or highly penetrating radiations that do not fit both criteria.

Why A is correct:

• Alpha particles are doubly positively charged helium nuclei, deflected toward the negative plate in an electric field per electrostatic force law (F = qE), and their high mass and charge limit range to ~few mm in air.

Why the others are wrong:

• B: Beta particles (electrons) have longer range (~meters in air) due to lower mass and charge.
• C: Gamma rays are neutral electromagnetic waves, undeflected by electric fields and penetrate far (>100 m in air).
• D: Identical to C; gamma rays lack charge for deflection and have high penetration.

Final answer: A