Question

Identify the two-dimensional shape of the cross-section if the cube shown is sliced horizontally.

Answer 1

Your question cannot be answered here because the cube has to be shown online... but the most common answer to this would be a rectangle... 

Answer 2

Sadly, the cube you promised us is not shown.

IF the cube is resting on the table in the normal way ... with
two of its faces horizontal and the other four faces vertical,
then any horizontal or vertical slice is a square.

You know what's fun ? Try doing this problem with cubes of
chocolate cake, and after you make slices, look at them and
then eat them.