Which nitrogen trihalide is the least basic?

In which of the following arrangements,the sequence is not strictly according to the property written against it?

Which of the following oxyacids is the strongest acid?

$PCl_{5} + P_{4}O_{10} \xrightarrow{\Delta } X$. The product $(X)$ is an oxygen-containing compound. How many moles of an oxyacid are formed on the complete hydrolysis of $1 \text{ mole}$ of $(X)$?

Nitrogen dioxide cannot be obtained by heating:

Dilute nitric acid on reaction with silver liberates