(c) $r = \frac{\sqrt{2mK}}{qB} \Rightarrow q \propto \sqrt{mK}\ \Rightarrow K \propto \frac{q^{2}}{m}$
$\Rightarrow \frac{K_{\alpha}}{K_{p}} = \left( \frac{q_{\alpha}}{q_{p}} \right)^{2} \times \frac{m_{p}}{m_{\alpha}} \Rightarrow \frac{K_{\alpha}}{8} = \left( \frac{2q_{p}}{q_{p}} \right)^{2} \times \frac{m_{p}}{4m_{p}} = 1$
$\Rightarrow K_{\alpha} = 8\ eV$