A drawing sheet changes when you draw a picture on it. Can you reverse this change?

It is all depends on situations:
• By erasing the drawing we can undo the change. For example, if we draw with the help of pencil, we can erase the drawing by using an eraser. Then, it is a reversible change.
• If we draw using a pen, we cannot erase the drawing. Then this change cannot be reversed, so it is irreversible change.

https://www.tiwariacademy.com/ncert-solutions/class-6/science/chapter-6/