How many moles of oxygen are in 25.45 g of caco3?

From the periodic table:

mass of oxygen = 16 grams

mass of calcium = 40 grams

mass of carbon = 12 grams

mass of CaCO3 = 40 + 12 + 3 (16) = 100 grams

Therefore, each 100 grams of CaCO3 contains 3 moles of oxygen

To know the number of oxygen moles in 25.45 grams, we will simply do cross multiplication as follows:

number of oxygen moles = (25.45 x 3) / 100 = 0.7636