1. Avogadro's Number

* Avogadro's number is a fundamental constant in chemistry that relates the number of particles (atoms, molecules, ions, etc.) in a mole.

* One mole of any substance contains 6.022 x 10^23 particles.

2. Setting up the Conversion

We can use Avogadro's number as a conversion factor to go from molecules to moles:

```

(9.02 x 10^23 molecules Cl2) * (1 mole Cl2 / 6.022 x 10^23 molecules Cl2)

```

3. Calculation

The "molecules Cl2" units cancel out, leaving us with moles of Cl2:

```

= 1.50 moles Cl2

```

Therefore, there are 1.50 moles of chlorine gas (Cl2) in 9.02 x 10^23 molecules.