Answer :
If you have a 39.4 mg sample of Selenium, it would consist of approximately 0.000498 moles, or about 2.997 x 10^20 atoms.
To figure out the amount of moles and atoms in a sample of Selenium, we first need to know the atomic weight of Selenium, which is approximately 78.96 g/mol.
First, convert the weight from milligrams (mg) to grams (g) by dividing by 1000. So, 39.4 mg becomes 0.0394 g.
Next, find the number of moles of Selenium. Moles = mass(g) / atomic weight(g/mol). So, in this case, Moles = 0.0394 g / 78.96 g/mol = 0.000498 moles.
To find the number of atoms, multiply the number of moles by Avogadro's Number, 6.022 x 10^23. The number of atoms = moles x Avogadro's Number = 0.000498 moles x 6.022 x 10^23 = 2.997 x 10^20 atoms.
Learn more about Moles and Atoms Calculation here:
https://brainly.com/question/30641974
#SPJ1