Which method is used to produce nitric acid?

In which of the following compounds does hydrolysis take place through $S_N^1$ and $S_N^2$ mechanisms respectively?

Which of the following statements is true regarding nitrogen?

Assertion : Although $PF_5, PCl_5$ and $PBr_5$ are known,the pentahalides of nitrogen have not been observed.
Reason : Phosphorus has lower electronegativity than nitrogen.

Which of the following statements is $NOT$ true?

Which of the following is the formula for metaphosphoric acid?