The penetrating powers of $\mathrm{\alpha }$ and $\mathrm{\beta }$ and $\mathrm{\gamma }$ radiations, in decreasing order, are

$$\begin{gathered} \mathrm{\gamma } \mathrm{radiations} \mathrm{are} \mathrm{EM} \mathrm{waves} \mathrm{with} \mathrm{zero} \mathrm{rest} \mathrm{mass} \mathrm{and} \mathrm{neutral} \mathrm{in} \mathrm{charge}. \mathrm{Hence} \mathrm{they} \mathrm{have} \mathrm{high} \mathrm{penetrating} \mathrm{power}. \\ \mathrm{\beta } \mathrm{radiations} \mathrm{are} \mathrm{lighter} \mathrm{than} \mathrm{\alpha }, \mathrm{and} \mathrm{also} \mathrm{carry} \mathrm{less} \mathrm{charge} \mathrm{than} \mathrm{\alpha }. \mathrm{Hence} \mathrm{\beta } \mathrm{has} \mathrm{more} \mathrm{penetrating} \mathrm{power} \mathrm{than} \mathrm{\alpha }. \end{gathered}$$