D.5 The number before the decimal point is not a zero, therefore, it is significant. All numbers after the zero are significant as well because the 1 followed by 3 zeros indicates the place of the numbers (hundreds, thousandth, ten thousandths.)
There are 5 significant digits. Significant digits are those that can be measurable - it indicates the accuracy of the measuring or the instrument of measuring. If the number is represented with four decimal numbers it means that the instrument is sensitive up to that detail in the measuring.
