1. The reaction is CaCO$_3 \to$ CaO + CO$_2$ (decomposition by burning).
2. Purity 90%, so effective mass = 0.9 \times 10 = 9 g.
3. Molar mass CaCO$_3$ = 100 g/mol, moles = 9 / 100 = 0.09 mol.
4. 1 mol CaCO$_3$ produces 1 mol CO$_2$, so 0.09 mol CO$_2$.
5. At STP, volume = moles \times 22.7 L/mol = 0.09 \times 22.7 \approx 2.043$ L \approx 2.044 L.
6. Therefore, the correct option is (3) 2.044 L.