Answer:
The answer to your question is 1.67 moles
Step-by-step explanation:
Data
moles of AlCl₃ = ?
moles of MgCl₂ = 2.5 
Balanced chemical reaction
 2Al + 3MgCl₂ ⇒ 2AlCl₃ + 3Mg
Process
To solve this problem using proportions and cross multiplication.
Use the coefficients of the balanced chemical reaction.
 3 moles of MgCl₂ ------------------- 2 moles of AlCl₃
 2.5 moles of MgCl₂ ----------------- x
 x = (2.5 x 2) / 3
-Simplification
  x = 5 / 3
-Result
  x = 1.67 moles