Given the equation CaO + H2O = Ca(OH)2 if you start with 1.86 moles of CaO, how many moles of Ca(OH)2 will result?
Look at the equation.
The equation tells you 1 mol CaO reacts with 1 mol H2O to yield 1 mol Ca(OH)2.
The equation tells you 1 mol CaO reacts with 1 mol H2O to yield 1 mol Ca(OH)2.