Final answer:
To determine the number of moles of MgCO3 in 252.939 grams, divide the mass by its molar mass, which is 84.31 g/mol. The calculation reveals there are 3.0 moles of MgCO3 in the given mass.
Step-by-step explanation:
To determine how many moles of MgCO3 are present in 252.939 grams of MgCO3, we need to use the molar mass of MgCO3. The molar mass can be calculated by adding the atomic masses of magnesium (Mg), carbon (C), and three oxygen atoms (O). The molar mass of MgCO3 is approximately 24.31 (Mg) + 12.01 (C) + (3 × 16.00) (3O) = 84.31 g/mol.
To find the number of moles, we divide the given mass by the molar mass:
Number of moles = mass of MgCO3 / molar mass of MgCO3 = 252.939 g / 84.31 g/mol = 3.0 moles
Therefore, the answer is (b) 3.0 moles of MgCO3.