Jay painted the inner four walls of a box. Then he put an ice block into it such that it did not touch the walls, but he couldn't do the same when he put water in that box. Why?

Liquid takes the shape of container, so it will always touch the walls of the box in which you put it.

Explanation:

We know that a solid has a definite shape and a definite volume hence it occupies only its own volume in the box, it does not touch the walls of the box.

However, a liquid does not have a definite shape and volume. It occupies the volume of the box. Therefore, the liquid water must definitely touch the walls of the box.