The stoichoimetric ratio of lead to lead oxide is 2:2. Given 451.4 grams of lead, we get the moles multiply by 2/2 or 1 and the molar mass of lead oxide, we get a product of 486.26 g lead oxide. The percent yield is the actual amount, 356.7 grams over 486.26 grams which is equal to 73.36% yield.