# A compound contains 14.5 g of magnesium and 3.5 g of oxygen. What is the mass percent of oxygen in the compound?

$19. \dot{4}$%
Mass ercentage states how much of a compound's mass is made up of something. In this case m_p=("mass of element")/("mass of whole compound")*100=3.5/(14.5+3.5)*100=3.5/18*100=7/36*100=19.dot4%.