10gm hydrogen =5mole hydrogen
64gm Oxygen =2mol mole oxygen
According to the reaction,
4gm hydrogen react with 32gm oxygen
10gm hydrogen react with 80gm oxygen
We only gave 64 grams of oxygen, indicating that oxygen is the limiting reagent.
All oxygen reat then 8gm hydrogen react and form 4mole of water .
Correct option is C