Calcium carbide reacts with water, $\mathrm{CaC}{}_2+2\mathrm{H}{}_2\mathrm{O}\to \mathrm{Ca}(\mathrm{OH}){}_2+\mathrm{C}{}_2\mathrm{H}{}_2$, and the acetylene is then burnt completely, $2\mathrm{C}{}_2\mathrm{H}{}_2+5\mathrm{O}{}_2\to 4\mathrm{CO}{}_2+2\mathrm{H}{}_2\mathrm{O}$. Starting with $6.4\mathrm{g}$ of pure $\mathrm{CaC}{}_2$ (Ca = 40, C = 12, O = 16, H = 1; $22.4\mathrm{L}\mathrm{mo}{\mathrm{l}}^{-1}$ at STP), which of the following statements is/are correct?

1. AThe $\mathrm{CO}{}_2$ obtained on complete combustion is $8.96\mathrm{L}$ at STP.
2. BThe mass of $\mathrm{Ca}(\mathrm{OH}){}_2$ formed in the first step is $7.4\mathrm{g}$.
3. CThe oxygen needed to burn all of the acetylene is $5.60\mathrm{L}$ at STP.
4. DThe acetylene liberated in the first step occupies $2.24\mathrm{L}$ at STP.