Methyl iodide reacts with water to form methanol and HI. If the reaction has 25% yield, how much methyl iodide must be added to water in order to produce 0.10 mole of methanol?
25 percent of actually formed is what we get..
So 0.40 moles of methanol is formed.
For that 0.40 moles of methyl iodide must react.