C: 6.0000
-To find significant figures, you always start by counting the FIRST NON-ZERO DIGIT in the number.
-Non-Zero digits are ALWAYS significant figures
A is a whole number, and has no decimal points, so you would count the first and last non-zero digits (5 and 2). If there were any zeros in between these numbers (eg. 302) we would also count them, but since all the zeros are BEHIND the last non zero digit (2) we DON'T count them. This leaves only two significant figures.
B, C, and D are all decimals, so the rules for counting are slightly different. Again, you start by counting the FIRST non zero digit, even if it is after the decimal (like in D) and you finish counting at the LAST digit in the number, even if it is a zero.
B, we would count 8, 0, 0, 2. This is only 4 significant figures.
D, we would count 2, 3, 5, 0. It doesn't matter that the 2 is behind the decimal, since all non-zero numbers are significant figures. The 0 at the end also counts because it is the last digit in the number. This is still only 4 significant figures.
This leaves only C!
C, we would count 6, 0, 0, 0, 0.
6 is the first non-zero digit, and since it is a decimal we go all the way to the last digit, aka 0. This counts 5 significant figures.