We know that $r=\frac{m v}{q B}=\frac{(2 m K)^{1 / 2}}{q B}$
$\therefore r_{p}=\frac{\left(2 m_{p} K_{p}\right)^{1 / 2}}{q_{p} B}$ and $r_{\alpha}=\frac{\left(2 m_{\alpha} K_{\alpha}\right)^{1 / 2}}{q_{\alpha} B}$
Now $\frac{r_{p}}{r_{\alpha}}=\sqrt{\left(\frac{m_{p}}{m_{\alpha}}\right)} \times \frac{q_{\alpha}}{q_{p}}=\sqrt{\left(\frac{m_{p}}{4 m_{p}}\right)} \times \frac{2 e}{e}=1$

$(A)$ $\vec{B}(x, y)$ is perpendicular to the $x y$-plane at any point in the plane
$(B)$ $|\vec{B}(x, y)|$ depends on $x$ and $y$ only through the radial distance $r=\sqrt{x^2+y^2}$
$(C)$ $|\vec{B}(x, y)|$ is non-zero at all points for $r$
$(D)$ $\vec{B}(x, y)$ points normally outward from the $x y$-plane for all the points between the two loops


