Question

Given P = 0.0030 m, Q = 2.40 m, R = 3000 m. Significant figures in P, Q, and R are respectively
A. 2,2,1
B. 2,3,4
C. 4,2,1
D. 4,2,3

Answer 1

Hint: Significant figures are nothing but the digits that we know with certainty along with the uncertain ones. Zeros coming before to first non-zero digit are
Insignificant. Zeros at the end of the right-hand side of a number are significant, if and only if they are on the right side of the decimal point.

Complete Step by Step Solution:
- In this question, we are provided with three measurements in metres having the decimal point at different positions.

We have to figure out the significant numbers.
- The lengths are 0.0030, 2.40, and 3000.
- There are various rules for significant figures.
- One rule states that all non-zero digits are significant.
- Without considering the decimal point, we get that in 2.40 m, 2 is a significant number and
in 3000 m, 3 is a significant number.
- One rule states that zeros preceding the first non-zero digit carry no significance.
- This zero only reveals the position of the decimal point. Therefore, 0.05 has one significant figure and 0.0035 has two significant figures. So, in 0.0030 m, 3 is a significant number.
- The two zeros present before 3 are insignificant.
- Zeros at the end or right-hand side of a number are significant, if and only if they are on the right-hand side of the decimal point. For example, 0.400 has one significant number.
- These two rules say that 0.0030 has two significant numbers. 2.40 m has three significant numbers. 3000 m has four significant numbers.
- Therefore, there are 2, 3, and 4 significant numbers in 0.0030 m, 2.40 m, and 3000 m.
So, option B is correct.

Note: It must be noted that zeros that exist in between two non-zero digits have significance. Accordingly, 5.006 contains four significant figures. 35.006 has five significant numbers.