ANS:A - 40

To calculate the percentage of calcium (Ca) by weight in CaCO3 (calcium carbonate), you need to consider the atomic masses of calcium (Ca) and carbon (C), as well as the molecular formula of calcium carbonate. The molar mass of calcium carbonate (CaCO3) is calculated as follows:

• Calcium (Ca): Atomic mass = 40.08 g/mol
• Carbon (C): Atomic mass = 12.01 g/mol
• Oxygen (O): Atomic mass = 16.00 g/mol (there are 3 oxygen atoms in CaCO3)

So, the molar mass of CaCO3 = (1 * 40.08) + (1 * 12.01) + (3 * 16.00) = 100.09 g/mol Now, to find the percentage of calcium (Ca) by weight in CaCO3, you divide the atomic mass of calcium by the molar mass of CaCO3 and multiply by 100: Percentage of Ca = (40.08 / 100.09) * 100 ≈ 40% Therefore, CaCO3 contains approximately 40% of calcium (Ca) by weight.