The correct formula for nitrogen dioxide is: 

 

Knowing the names of all the compounds in the possibilities is necessary to arrive at the solution. Nitrogen dioxide, nitric oxide, dinitrogen monoxide, and dinitrogen pentoxide are these substances.

The given compound is nitrogen dioxide. Here, nitrogen means one molecule of nitrogen ($\mathrm{N}$) and dioxide can be broken down as “di” indicates two, and oxide represents oxygen ($\mathrm{O}$) molecules i.e. it contains two molecules of oxygen.

Here, the terms "nitrogen" and "dioxide" refer to one and two nitrogen molecules, respectively, as well as one and two oxygen molecules, respectively.

Therefore, the correct formula for nitrogen dioxide is ${\mathrm{NO}}_2$.

Hence option (C) is correct.