Which of the following oxyacids has an $X-O-X$ linkage?

White phosphorus reacts with thionyl chloride to give

The laughing gas is

Discuss the anomalous behaviour of nitrogen.

Given below are two statements: one is labelled as Assertion $(A)$ and the other is labelled as Reason $(R)$.
Assertion $(A)$ : $PH_3$ has lower boiling point than $NH_3$.
Reason $(R)$ : In liquid state $NH_3$ molecules are associated through van der Waals forces,but $PH_3$ molecules are associated through hydrogen bonding.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which among the following oxides of nitrogen is a brown-coloured gas?