A proton is projected with a speed of $2 \times 10^{6}(\mathrm{~m} / \mathrm{s})$ at an angle of $60^{\circ}$ to the $\mathrm{X}$ -axis. If a uniform mag. field of $0.104$ tesla is applied along $\mathrm{Y}$ -axis, the path of proton is
(a) A circle of $\mathrm{r}=0.2 \mathrm{~m}$ and time period $\pi \times 10^{-7} \mathrm{sec}$
(b) A circle of $\mathrm{r}=0.1 \mathrm{~m}$ and time period $2 \pi \times 10^{-7} \mathrm{sec}$
(c) A helix of $r=0.1 \mathrm{~m}$ and time period $2 \pi \times 10^{-7} \mathrm{sec}$
(d) A helix of $\mathrm{r}=0.2 \mathrm{~m}$ and time period $4 \pi \times 10^{-7} \mathrm{sec}$