Consider the motion of a positive point charge in a region where...

If $\theta=0^{\circ}$, the charged particle is projected along $x$-axis, due to magnetic field, $\vec{B}$ the charged particle will tend to move in a circular path in $y-z$ plane but due to force of electric field $\vec{E}$, the particle will move in a helical path with increasing pitch. Hence options (A) and (B) are wrong. If $\theta=10^{\circ}$, we can resolve velocity into two rectangular components. One along $x$-axis \left(v \cos 10^{\circ}\right)$and one along$y$-axis \left(v \sin 10^{\circ}\right)$. Due to $v \cos 10^{\circ}$, the particle will move in circular path and due to $v \sin 10^{\circ}$ plus the force due to electric field, the particle will undergo helical motion with its pitch increasing. If $\theta=90^{\circ}$, the charge is moving along the magnetic field. Therefore the force due to magnetic field is zero. But the force due to electric field will accelerate the particle along $y$-axis.