$\alpha$ particles are positively charged He nucleus, it can accept $2 \mathrm{e}^{-}, \beta$ rays are negatively charged which are similar to $\mathrm{e}^{-}$, can donate $1 \mathrm{e}^{-}, \gamma$ are radiations. Hence ionisation power of $\alpha$ is maximum. $\gamma$ are most energetic and $\propto$ is least energetic $\therefore$ Penetration power of $\gamma$ is maximum.