Question

al(s) + cl₂(g) → alcl₃(s)

Explanation:

Step1: Balance Al atoms

Left: 1 Al; Right: 1 Al → already balanced.

Step2: Balance Cl atoms

Left: 2 Cl; Right: 3 Cl → LCM=6. Multiply Cl₂ by 3, AlCl₃ by 2:
$\text{Al}(s) + 3\text{Cl}_2(g)
ightarrow 2\text{AlCl}_3(s)$

Step3: Rebalance Al atoms

Right: 2 Al; Left:1 Al → Multiply Al by 2:
$2\text{Al}(s) + 3\text{Cl}_2(g)
ightarrow 2\text{AlCl}_3(s)$

Answer:

$2\text{Al}(s) + 3\text{Cl}_2(g)
ightarrow 2\text{AlCl}_3(s)$