An electron and a proton are moving on straight parallel paths with...

$\quad r=\frac{m v}{B q}$ or $\quad r \propto m\therefore r_e \lt r_p$ as $m_e \lt m_p$ Further, $\quad T=\frac{2 \pi m}{B q}$ or $\quad T \propto m$
$$\begin{aligned} \therefore \quadT_e & < T_p \\ t_e & =\frac{T_e}{2} \end{aligned}$$and or $\quad t_e \lt t_p\therefore$ Correct options are (b) and (d). Note In JEE 2011, official answer key, correct options were given bc, bd, bcd, here student should realise that both the electron and proton enter the magnetic field at the same time or at different times. Analysis of Question (i) Question is simple. (ii) In the situation given above particle will never complete the circle unless magnetic field is all around.