Verified Answer :

it 1:1 I had an online review and thats the answer it told me it was.
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Answer : The mole ratio of \(PCl_3\) to \(PCl_5\) is 1 : 1 ratio.

Explanation :

The balanced reaction will be,

\(PCl_3+Cl_2\rightarrow PCl_5\)

From the balanced reaction, we conclude that

1 mole of \(PCl_3\) react with the 1 mole of \(Cl_2\) to give 1 mole of \(PCl_5\)

Hence, the mole ratio of \(PCl_3\) to \(PCl_5\) is 1 : 1 ratio.