Chemistry help

Question

3. A metal carbonate containing an unknown +2 metal ("MCO3") reacts with excess acid resulting in the loss of CO2. Analysis of the experimental data indicates that the mass % CO2 in the unknown metal carbonate is 30%. Which of the metal cations below is most likely to be the unknown metal in the original metal carbonate?

Answer 1

MCO3 + 2HCl ==> MCl2 + H2O + CO2

You neglected to include the list of metal carbonates.  Look at the list and pick the one where 44/molar mass of the MCO3 is equal to 0.30.