An electromagnetic wave is propagating in the positive x direction. at a given moment in time, the magnetic field at the origin points in the positive y direction. in what direction does the electric field at the origin point at that same moment?

Along negative z axis

Explanation:

As we know that in any electromagnetic waves propagation the electric field component and magnetic field component is perpendicular to each other and the propagation of wave is perpendicular to both the components of waves.

so here it follows the condition that velocity is perpendicular to both electric field and magnetic field so we will have

since velocity is towards positive x direction and magnetic field is towards positive y direction so for the above condition to be hold good the electric field must be along negative z direction.

28. evolution

29. environment, survive, offspring  

explanation: