This formula equation is unbalanced.

p4(s) + cl2(g) pcl3(l)

which coefficient should be placed in front of pcl3 to balance this equation?
1246

The answer is:  [C]:  "4" .

Note:  To balance this equation, the coefficient, "4", should be placed in front of the PCl₃ ;  and the coefficient, "6", should be placed in front of the Cl₂ .

The balanced equation is:

             P₄ (s) + 6 Cl₂ (g)  → 4 PCl₃ (l)   .