1. Find the molar mass of AlCl3:

* Aluminum (Al): 26.98 g/mol

* Chlorine (Cl): 35.45 g/mol (x 3 for three chlorine atoms)

* Total molar mass of AlCl3: 26.98 + (35.45 x 3) = 133.33 g/mol

2. Calculate the mass of chlorine in AlCl3:

* Mass of chlorine: (35.45 g/mol x 3) = 106.35 g/mol

3. Calculate the percent of chlorine:

* (Mass of chlorine / Molar mass of AlCl3) x 100%

* (106.35 g/mol / 133.33 g/mol) x 100% = 79.75%

Therefore, the percent of chlorine in AlCl3 is approximately 79.75%.