Mukhil is preparing square-shaped tiles for a mathematics display. Each tile has an integer side length. He notes down their areas and observes some interesting patterns in the last digits of those numbers.
1. Which of the following numbers is not a perfect square?
2. If the area of a square tile is 961 \(cm²\). Then, the length of one side \(=\) ____________ \(cm\).
3. A piece of cloth has an area of 300 \(cm²\). What is the greatest possible side length of a square that can be cut from it?
4. Which of these numbers both ends with the digit \(6\) and represents a perfect square?