Question

Which is the number of atoms in 4.5 moles of Hg, correctly written in scientific notation with the correct number of significant figures?
2.7 x 10^24
27 x 10^23
2.71 x 10^24
27.099 x 10^23

Answer 1

Answer: The correct answer is $2.7\times 10^{24}$

Explanation:

We are given:

Moles of mercury = 4.5 moles

According to the mole concept:

1 mole of an element contains $6.022\times 10^{23}$ number of atoms.

So, 4.5 moles of mercury will contain $4.5\times 6.022\times 10^{23}=27.099\times 10^{23}$ number of atoms.

The rule that must be applied for the multiplication and division in significant figures is:

The least number of significant figures in any number of the problem determines the number of significant figures in the answer.

Here, the least precise significant number in problem are 2. Thus, the answer must also contain 2 least significant numbers.

Therefore, the correct answer becomes $2.7\times 10^{24}$

Answer 2

2.7 x 10^24, since 4.5 has two significant figures.