2.17 x 1023 molecules Br2 → Moles

0.36moles

Explanation:

The number of moles of a substance can be calculated by dividing the number of atoms of such substance (nA) by Avagadro's number (6.02 × 10^23)

That is;

n = nA ÷ 6.02 × 10^23

number of moles = 2.17 x 10^23 ÷ 6.02 × 10^23

n = 2.17/6.02 × 10^(23 - 23)

n = 0.36 × 10°

n = 0.36moles