The correct answer to the question is : A) Alpha particle
EXPLANATION:
As per the question, we have three radioactive decay particles which are known as alpha particle,beta particle and gamma ray.
Out of these radioactive radiations, alpha particle and beta particle are material particles. Alpha particle is the doubly charged helium nucleus while beta particle is the stream of electrons.
Alpha and beta being material particles, their penetration depth is very lower.
Gamma ray is an electromagnetic radiations. Hence, its penetration effect is the most.
Out of alpha and beta particles, the size of alpha particle is more as compared to the size of beta particle. Hence, the penetration effect of alpha particle is less as compared to beta particle.
Hence, alpha particle has the lowest penetrating ability.
