Introduction to Nitric Acid

During thunderstorm, rain water contains nitric acid. Explain with reactions.

Nitrogen is known to form a variety of oxides and oxyacids. $\mathrm{NO}$ and ${\mathrm{N}}_2\mathrm{O}$ are unstable, while ${\mathrm{NO}}_2$ is a stable oxide. ${\mathrm{NO}}_2$ is a brown acidic gas at room temperature and on cooling below $20°\mathrm{C}$ gives ${\mathrm{N}}_2{\mathrm{O}}_4. {\mathrm{NO}}_2/{\mathrm{N}}_2{\mathrm{O}}_4$dissolves in water to give nitric acid. ${\mathrm{N}}_2{\mathrm{O}}_4$ reacts with $\mathrm{NO}$ to form ${\mathrm{N}}_2{\mathrm{O}}_3$. When some metals react with dil. ${\mathrm{HNO}}_3$ at room temperature, oxides of nitrogen in lower oxidation states are formed. The correct statement is

All of the given statements are true for nitric acid except

Nitric acid occurs in free state as Nitre.

How nitric acid occurs in free state?

Aqua regia contains one part by volume of hydrochloric acid and three parts by volume of nitric acid.

Which of the following metals does not dissolve in concentrated ${\mathrm{HNO}}_3$?

Which of the following is the naturally occurring nitrate?

Which of the following is the chemical formula of nitric acid?