Answer:
Option C is correct.
The electric-field vector must oscillate in the yz plane.
Step-by-step explanation:
Light, in waveform, is an electromagnetic wave.
And electromagnetic waves are known to have their electric and magnetic field perpendicular to each other and also simultaneously perpendicular to the direction of propagation of the wave.
If the velocity of direction of propagation of the wave is in one direction, the electric-field vector must be in a direction we are sure is perpendicular to this direction of wave propagation and the wave's magnetic field.
Of the options provided, only option B (z-direction) and option C (yz-plane) show a direction that is indeed perpendicular to the direction of propagation of the wave (x-axis).
And truly, the electric-field vector for this wave can be in any of the two directions without breaking the laws of physics, but the electric-field vector oscillating in the yz-plane is a more general answer as it covers all the possible directions that the electric-field can oscillate in, including the one specified by option B (z-direction).
Hence, the correct answer is option C.
Hope this Helps!!!