How many significant figures are there in 0.0025?

Question

Accepted Answer

The correct option is (2):

To determine the number of significant figures in a given number, we follow a set of rules. For numbers less than one (i.e., decimal numbers starting with zero), leading zeros are not considered significant. Leading zeros are those zeros that appear before the first non-zero digit. They are simply place holders that indicate the position of the decimal point. In the number $0.0025$, the first three zeros ($0.00$) are leading zeros. They do not contribute to the precision of the measurement and therefore are not significant. The significant figures begin from the first non-zero digit, which in this case is '2'. Following '2' is '5', which is also a non-zero digit. All non-zero digits are always significant. Therefore, in $0.0025$, only the digits '2' and '5' are significant. This means there are two significant figures in the number $0.0025$. Understanding these rules is crucial for calculations in chemistry and physics, as significant figures reflect the precision of a measurement.

The incorrect option is (1):
This option would imply that only one of the non-zero digits is significant, or that only one of the leading zeros (incorrectly) contributes to significance, which contradicts the rules of significant figures.

The incorrect option is (3):
This option suggests there are three significant figures. This would be correct if one of the leading zeros was considered significant, which is incorrect according to the rules of significant figures where leading zeros are not significant.

The incorrect option is (4):
This option suggests there are four significant figures. This would imply that all leading zeros are significant, which is incorrect as leading zeros are merely placeholders and do not convey precision.