Which of the carbonates given below is unstable in air and is kept in CO2, atmosphere to avoid decomposition?

(1) BeCO3 is unstable to the extent that it is stable only in an atmosphere of CO2. BeCO3 shows a reversible reaction because the stability of oxide formed is more than carbonates.BeCO3⇌BeO+CO2BeCO3 is unstable due to the strong polarising effect of small Be2+ ions on the large polarisable carbonation. Moreover, extra stability of the oxide achieved through lattice energy by packing small cation with a small oxide ion.