Think a little more..
you have 1.25e23 atoms, and there are 6.02e23 atom in one mole. dividing the first by the second yields 2.08e-1 mol Mg
A. 0.208 × 101 mol Mg
B. 2.08 × 101 mol Mg
C. 2.08 × 10 -1 mol Mg
D. 20.8 mol Mg
I think it would be D
you have 1.25e23 atoms, and there are 6.02e23 atom in one mole. dividing the first by the second yields 2.08e-1 mol Mg
the scientific notations cancel each other out and then we're only left with the numbers 1.25/6.02 which equals 0.208 rounded to the thousandth
0.208 = 2.08(10^-1) because negative notations means moving the decimal point to the left
The given question states that there are 1.25 × 10^23 atoms of magnesium. To convert this into moles, you divide the number of atoms by Avogadro's number.
1.25 × 10^23 atoms of magnesium / 6.022 × 10^23 atoms/mol = 0.207 moles of magnesium
So, the correct answer is A. 0.208 × 10^1 mol Mg.