Polarisation of light — UPSC CSE 1998 Physics PYQ

What was the basis for light to be accepted as an electromagnetic wave ? The \vec{E} vector in a light wave polarised in the (x, y) plane is expressed as \vec{E}(x, y, z, t) = \vec{E}_0 \sin\left[\omega t - k(x + y)\right] Determine the propagation and the polarisation vectors.