Determine the mass of calcium that will react with 4.8 g of oxygen if it is known that these elements

Determine the mass of calcium that will react with 4.8 g of oxygen if it is known that these elements combine in a mass ratio of 5: 2. Determine the mass of the compound obtained.

From the mass ratio of elements, we find the oxide formula, knowing the molecular weights of O (16 amu) and Ca (40 amu).
Since 40: 16 = 5: 2, you can define the oxide formula as CaO.
Then the reaction goes like this: 2Ca + O2 = 2CaO.
Oxygen reacted 4.8: 32 = 0.15 mol, and calcium was twice as much, 0.15 * 2 = 0.3 mol. Its mass
is equal to 0.3 mol * 40 g / mol = 12 g.