Given below are two statements. One is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : A electron in a certain region of uniform magnetic field is moving with constant velocity in a straight line path. Reason (R): The magnetic field in that region is along the direction of velocity of the electron. In the light of the above statements, choose the correct answer from the options given below :

Assertion (A): An electron moves with constant velocity in a straight line in a uniform magnetic field.

The magnetic force on a moving charge is $$\vec{F} = q\vec{v} \times \vec{B}$$. If $$\vec{v} \parallel \vec{B}$$, then $$\vec{v} \times \vec{B} = 0$$ and the force is zero, so the electron moves in a straight line with constant velocity. TRUE.

Reason (R): The magnetic field is along the direction of velocity of the electron.

This is exactly the condition that makes the cross product zero. TRUE.

R correctly explains A: when $$\vec{B} \parallel \vec{v}$$, there is no magnetic force, so the electron travels in a straight line.

The correct answer is Option C: Both (A) and (R) are true and (R) is the correct explanation of (A).