What is the percent composition of O in LiOH?

The formula shows that oxygen is one atom out three in the formula unit, so that the atomic percent of oxygen in the compound is 33.333.......... By adding the gram atomic masses of the three elements, one obtains 23.95 as the gram formula mass, to the justified number of significant digits (the four digits in the value for the gram atomic mass of lithium), and 100 (15.9994/23.95) is 66.80 percent by mass of oxygen in LiOH.