Consider the reaction represented by the following equation:  x Al  +  yCl$_2$ → z AlCl$_3$

Analyze the question: You need to balance the equation x Al + y Cl₂ → z AlCl₃, so that the number of atoms of each element is the same on both sides.

Concept: Balancing means choosing coefficients so that atoms are conserved. Cl₂ is diatomic (2 Cl atoms per molecule), while AlCl₃ has 3 Cl atoms per formula unit. So we need a common multiple of 2 and 3, which is 6.

Step-by-step solution:

1. Balance Al: x = z
2. Balance Cl: 2y = 3z
3. Take the smallest whole numbers. If z = 2, then 2y = 6, so y = 3. Then x = 2.

The balanced equation is:

2Al + 3Cl₂ → 2AlCl₃

Check:

• Left: Al = 2, Cl = 3 × 2 = 6
• Right: Al = 2, Cl = 2 × 3 = 6 ✔

So x = 2, y = 3, z = 2.

Checking the options:

• A. 2, 3 and 2 ✔ (matches the balanced equation)
• B. 2, 2 and 3 ✘ (gives 4 Cl on the left and 9 on the right)
• C. 1, 2 and 1 ✘ (gives 4 Cl on the left and 3 on the right)
• D. 1, 1 and 1 ✘ (gives 2 Cl on the left and 3 on the right)

Exam tip: When one side has a diatomic molecule (like Cl₂, O₂, H₂) and the other has an odd number of that atom, find the LCM. Here the LCM of 2 and 3 is 6, so you need 3 Cl₂ and 2 AlCl₃. Always do a quick atom count to confirm.