Question

Significant figures in 0.00051 are:
(a) 5
(b) 3
(c) 2
(d) 4

Answer 1

Hint: Significant figures defines any significant digits from zero to nine which are wholly inclusive. There are some which are used to count the number of significant figures in a number. Here, using the rules, we have to count the significant figures of 0.00051.

Complete Step by Step Solution:
Let's discuss the four rules of counting significant figures. They are as follows:
1. All digits (non-zero) and the zeroes present in a number possessing the two non-zero digits on the sides are significant figures. For example, in 300042, three non-zero digits are present, and the three zeroes are present between 2 and 4. Therefore, significant figures in 300042 are six.

2. The zeroes used to determine the location of a decimal point are non-significant. For example, in 0.000034, there are two significant figures namely 3 and 4.

3. The zeroes present at the number's end and to the right-hand side of the decimal point are considered significant. For example, in the number 0.0002500, four significant figures are present. Here, the two zeroes at the end are also counted as significant.

4. If no decimal point is present, the zeroes at the end of the number are not counted as significant. For example, in 1900 only two significant figures were present: one and nine.

Now, come to the question. In the number 0.00051, two significant figures are present following the second rule.
Hence, option c is right.

Note: It is to be noted that, if a number is present in the form of scientific notation such as $N\times10^{x}$ , the N is considered significant and 10 and x are not significant. For example $52\times10^{4}$, only two significant figures present are 5 and 2.