A radioactive source emits three types of radiation.
a) Name the radiation of zero mass.
b) Name the radiation which has the lowest ionising power.
c) Name the radiation which has the lowest penetrating power.
d) Give the charge and mass of particles composing the radiation in part (c).

Radioactivity is a nuclear phenomenon of spontaneous emission of $\alpha$ (Alpha), $\beta$ (Beta) and $\gamma$ (Gama) radiations from the nucleus of atoms during their decay.
(a) Gamma radiation has zero mass as gamma rays are nothing but high energy electromagnetic waves.
(b) As gamma rays are massless and have high energy, they can pass through a medium without interacting and ionizing the medium much. Thus, gamma rays have the lowest ionizing power.
(c) Alpha particles have the maximum mass compared to other radiation. Alpha particles, due to their size, interact with medium particles most and lose energy very fast. This is why alpha particles have the lowest energy penetrating power.
(d) Alpha particle has positive charge = $3.2\times {10}^{-19}C$
Rest mass of the alpha particle = 4 times the mass of proton = $6.68\times {10}^{-27}kg$