Which element is not present in Nessler's reagent?

Which of the following statements is not true for nitrogen?

$(NH_4)_2Cr_2O_7$ on heating gives:

For the reaction $N_{2(g)} + O_{2(g)} \xrightarrow{\Delta} 2NO_{(g)}$,the temperature required is ........... $K$.

Given below are two statements:
Statement-$I$: Element '$X$' and '$Y$' are the most and least electronegative elements, respectively, among $N, As, Sb$ and $P$. The nature of the oxides $X_{2}O_{3}$ and $Y_{2}O_{3}$ is acidic and amphoteric, respectively.
Statement-$II$: $BCl_{3}$ is covalent in nature and gets hydrolysed in water. It produces $[B(OH)_{4}]^{-}$ and $HCl$ in aqueous medium.

The main products formed when copper metal is reacted with concentrated $HNO_3$ are