Explanation

(d) The direction of magnetic field is along the direction of motion of the charge particles, so angle will be $0{^\circ}.$
$\therefore Force\ F = qvB\sin\theta$
$\ \ \ \ \ \ \ \ \ \ \ = qvB\sin 0$
$\ \ \ \ \ \ \ \ \ \ \ \ = 0\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \left( \because\sin{0 = 0} \right)$
So, there will be no change in the velocity.