Explanation:
To solve this question, we need to know the Avogadro's constant:
6.022 x 10^23 atoms equal 1 mol.
So, in this case we have 4.35x10^24 atoms of selenium.
We first transform it to moles and then to grams, using the following formula:
m = n*MM
where:
m = mass
n = moles
MM = molar mass of selenium = 78.96 g/mol
6.022 x 10^23 ---- 1 mol
4.35x10^24 ---- x mol
x = 7.22 moles
m = 7.22 * 78.96
m = 570.4 g
Answer: m = 570.4 g
