5, 1, 2
5, 5, 2
5, 1, 5
4, 4, 2
Zeroes before a digit is not counted as a significant figure. In the first number, all digits are significant. In the second number, only 3 is significant; all other zeroes are before the digit and therefore not counted as a significant figure. Numbers in powers are also not counted as a significant number; hence there are only 2 significant digits in the last number. Therefore, option (A).