Answer:
+4
Step-by-step explanation:
Hello,
In this case, considering nitrogen dioxide's formula:
![NO_2](https://img.qammunity.org/2021/formulas/chemistry/college/fr6ouvbu4181g8uj71kgl3lnkijqnuj6wh.png)
And due to the fact that oxygen's oxidation state is -2 in this case, we could find nitrogen's oxidation state in nitrogen dioxide by using a balance charge:
![N^(+x)O_2^(-2)\\x-4=0\\x=4](https://img.qammunity.org/2021/formulas/chemistry/high-school/grxqdobsvuxf09jfxazzz2b1edx1sjul4j.png)
For that reason, nitrogen's oxidation state is +4:
![N^(+4)O_2^(-2)](https://img.qammunity.org/2021/formulas/chemistry/high-school/rn79ftpbp2amk6b30f6gu9txupqqla1pjk.png)
Best regards.