Question

0 pcl₃ → 0 p₄ + 0 cl₂

Explanation:

Step1: Balance phosphorus atoms

Start with unbalanced equation: $\text{PCl}_3
ightarrow \text{P}_4 + \text{Cl}_2$
Add coefficient 4 to $\text{PCl}_3$ to match 4 P on right:
$4\text{PCl}_3
ightarrow \text{P}_4 + \text{Cl}_2$

Step2: Balance chlorine atoms

12 Cl on left, add coefficient 6 to $\text{Cl}_2$:
$4\text{PCl}_3
ightarrow \text{P}_4 + 6\text{Cl}_2$

Step3: Verify atom counts

Left: 4 P, $4\times3=12$ Cl
Right: 4 P, $6\times2=12$ Cl. Balanced.

Answer:

Left box: $4\text{PCl}_3$
Right box: $\text{P}_4 + 6\text{Cl}_2$