4.28 x 10^24 molecules of chlorine gas to moles of chlorine gas.

7.1 moles Cl₂

Explanation:

To solve this problem we will use Avogadro's number (Aₙ), which tells us how many molecules (or atoms) are present in 1 mol of any given substance

Aₙ = 6.023 x 10²³ molecules/mol

With that in mind now we proceed to convert molecules into moles:

4.28 x 10²⁴ molecules Cl₂ ÷ 6.023 x 10²³ molecules/mol = 7.1 moles Cl₂