In the Serpeck process, silica-rich bauxite is heated with coke in a stream of nitrogen at about $1800\mathrm{K}$. The aluminium compound formed, which is then hydrolysed with water to give $\mathrm{Al}(\mathrm{OH}){}_3$ and a gas, is

1. A$\mathrm{Al}{}_4\mathrm{C}{}_3$, the gas being $\mathrm{CH}{}_4$
2. B$\mathrm{AlN}$, the gas being $\mathrm{N}{}_2$
3. C$\mathrm{Al}(\mathrm{NO}{}_3){}_3$, the gas being $\mathrm{NO}{}_2$
4. D$\mathrm{AlN}$, the gas being $\mathrm{NH}{}_3$