The velocity of an EM wave in a given medium is $V = 3 × 10^7\hat j$. When electric field oscillates along z-axis, then direction of oscillation of magnetic field at that time should be:

+x-axis

The correct answer is Option (4) → +x-axis

Since the wave velocity $(v)= 3 × 10^7\hat j$ indicates that the wave is travelling along the y-axis, we can apply the right hand rule-

∴ Also, if electric field is along positive z-axis, the magnetic field B will oscillate along z-axis.