Question

# $\gamma$rays has least penetrating power.A) TrueB) False

Hint: The penetrating power decreases with increase in the mass of the particle. Gamma rays are not particle rays so they do not have mass.

Gamma rays are not particles. They are high energy electromagnetic radiations. They are more powerful than X rays. Gamma rays do not have either mass or charge. They have huge penetration power. To shield gamma rays, several inches of dense material (such as lead) is required. Gamma rays can pass through human body without striking anything. The ionizing power of gamma rays is least.
Alpha particles can be shielded with paper skin. Beta particles can be shielded with aluminium foil.

Three different types of radiation are $\alpha ,\beta {\rm{ and }}\gamma$ rays. Among these, the $\alpha$ particles have maximum mass. The mass of $\beta$ particles is much smaller than that of the $\alpha$ particles. The $\gamma$ rays do not have mass.

The penetrating power is the ability of the radioactivity to pass through materials.
The penetrating power decreases with increase in the mass of the particle. Bigger particles have more chances of collisions with the atoms of material. Due to the collision, the particle will stop and it will not pass through the material.

The penetrating power of $\alpha$ particles is the least whereas the penetrating power of $\gamma$ rays is maximum. Thus, the given statement is false.

Hence, option B) is the correct answer.

Note:
Do not mix penetrating power with ionization ability. The ionization ability increases with increase in charge on the particle.