#### Answer

The number of significant figures in each number:
(a) Number of significant figures is 9. But the number is not exact because calculating the exact population is not possible.
(b) Number of significant figures is 3. This is an approximate value and not the exact conversion.
(c) Number of significant figures is 3. This is also an approximate value and not the exact value of density.
(d) This is an exact number because a dozen is equal to 12. So, it has an unlimited number of significant figures.

#### Work Step by Step

The significant figures of a number are digits that make the measurement more precise. This includes all digits except
1. All leading zeros.
2. Trailing zeros when they only indicate the scale of the number.
3. All extra digits that are introduced to make the calculations carried out more precise than the original data.
Exact numbers have affixed value that cannot change. Defined quantities have an unlimited number of significant figures.
The number of significant figures in each number:
(a) Number of significant figures is 9. But the number is not exact because calculating the exact population is not possible.
(b) Number of significant figures is 3. This is an approximate value and not the exact conversion.
(c) Number of significant figures is 3. This is also an approximate value and not the exact value of density.
(d) This is an exact number because a dozen is equal to 12. So, it has an unlimited number of significant figures.