Determine the theoretical and percent yield of hydrogen gas if 78.5 g water undergoes electrolysis to produce hydrogen and oxygen and 3.63 g hydrogen is collected?

First, find the theoretical yield.

Do as follows:
Write and balance the equation.
Convert 78.5 g H2O to moles. moles = grams/molar mass
Convert moles H2O to moles H2 using the coefficients in the balanced equation.
Convert moles H2 to grams. g = moles x molar mass. This is the theoetgical yield in grams. Call that T. E.
%yield = (actual yield/T. E.)*100 = ?