10. Which number when divided by it, will leave the other number unchanged? a) 1 b) 2 c) 5

The number that when divided by it leaves the other number unchanged is \(1\). When you divide any number by \(1\), the result is the number itself (e.g., \(x \div 1 = x\)). In contrast, dividing by \(2\) or \(5\) would change the value of the number. So, the answer is: **a) 1**