Question

The prism is cut by a plane that is parallel to the bases of the prism and perpendicular to the height h. What is the shape of the intersection of the prism and the plane? rectangle with unequal sides triangle square trapezoid

Answer 1

It depends on what prism it is.

If it's a triangle prism, the shape is a triangle.

If it's a square prism, the shape is a square.

If it's a trapezoidal prism, the shape is a trapezoid.

Answer 2

Based on the image above, the cross-section will be a triangle. 

Imagine you have a slice of cake, which has the same shape as the image, and you cut along one of the layers (perpendicular to height, parallel to the base). 
The cross section of this cut will be a triangle, and the two resulting pieces will have the same general shape as the original slice