Answer:
In the reaction you would have 15.0 mols of Y and X.
Step-by-step explanation:
The stoichiometric coefficents for X and Y are 1 and 2 respectively, if you start the reaction with 10.0 moles of Y you would need 5.0 moles of X in order to achieve a complete reaction so you will have 15.0 total moles in the reaction, assuming no mass loss and no nuclear reactions.