Which of the following statements is not correct regarding the gas evolved by the reaction of dilute HCl on $\mathrm{CaCO}_3$ ?

Which of the following gives more number of oxides on reacting with HCl ?

Which of the following statements is not correct?

Boron trifluoride on reaction with lithium aluminium hydride in ether gives $\mathrm{LiF}^{\circ} \mathrm{AlF}_3$ and $X . X$ on reaction with $\mathrm{NH}_3$ gives $Y$. $Y$ on further heating gives a compound $Z$. The number of $\sigma$-bonds and $\pi$-bonds in $Z$ are $x$ and $y$ respectively. $(x+y)$ is equal to