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) .
______________________________________________________
