K⁺ ion is a constituent of sodium pump.

Solubility of alkaline earth metal sulphates decreases down the group because hydration energy decreases.

Carbonates becomes more thermally stable down the group, Also, the alkali metal carbonate are more stable than alkaline earth metal carbonates. Therefore MgCO₃ will leave CO₂ easily.

MgCO₃ $$\buildrel \Delta \over \longrightarrow $$ MgO + CO₂

MgCO₃ $$\buildrel \Delta \over \longrightarrow $$ MgO + CO₂

84 g of MgCO₃ $$ \equiv $$ 40 g of MgO

$$ \therefore $$ 20 g of MgCO₃ = $${{40} \over {84}} \times 20$$ = 9.52 g of MgO

But Actual yield = 8 g of MgO

$$ \therefore $$ % purity = $${8 \over {9.52}} \times 100$$ = 84%