Which of the following is thye approximate number of atoms i9n 100g of astatine (At)

A. 1.26X10 23th power
B. 2.87X10 23th power
C. 6.02X10 23th power
D. 1.26X10 24th power

First find the moles of At in 100 g

moles = mass / Molar Mass

100 g / 210 g/mol

= 0.47619 moles

To find the number of atoms multiply moles by 6.023 x 10^23 particles per mole

0.47619 mol x 6.023 x 10^23 = 2.87 x 10^23 atoms

B

At-210 is the most stable isotope, so you have 100/210 moles of At.

(100/210)(6.023x10^23) = 2.87x10^23