I need help.. this one question says explain why the measurement "12.5 * 10^-6 centimeters" is written in correctly in scientific notation.. is it because it is not necessary to have the centimeters in there?

No, scientific notation is ALWAYS the first digit followed by the decimal point followed by x 10 to the some power.

So 12.5 x 10^-6, although a correct number probably, is 1.25 x 10^-5 in scientific notation.