The correct option is C 4 mol of R
2P+Q⟶R
When 5 moles of Q is taken, it would require 10 moles of P to yield 5 moles of the product R. Here, only 8 moles of P are available, so P is the limiting reagent.
So 8 moles of P will react with 4 moles of Q to yield 4 moles of the product R. The remaining 1 mole of Q is left unreacted.