Which of the following nitrogen trihalides is the weakest base?

$HNO_3 + P_4O_{10} \to 4HPO_3 + X$. $X$ is

Which of the following statements are correct about the reaction between the copper metal and dilute $HNO_3$?
$(I)$ The principal reducing product is $NO$ gas.
$(II)$ $Cu$ metal is oxidised to $Cu^{2+}$ (aq.) ion which is blue in colour.
$(III)$ $NO$ is paramagnetic and has one unpaired electron in antibonding molecular orbital.
$(IV)$ $NO$ reacts with $O_2$ to produce $NO_2$ which is linear in shape.
Choose the correct statements.

Which one of the following is not a colourless compound?

Which gas is used in the manufacturing of nitrogenous fertilizers?

Which of the following statements is $NOT$ correct?