Nitrogen and oxygen can form several different compounds due to a combination of factors:

* Variable valency: Both nitrogen and oxygen can exhibit multiple oxidation states (valencies). Nitrogen can have valencies of -3, -2, -1, +1, +2, +3, +4, and +5, while oxygen typically has valencies of -2 and -1. This allows for a wide range of possible combinations.

* Multiple bonding possibilities: Nitrogen and oxygen can form single, double, and triple bonds with each other. This adds further complexity to the types of compounds that can be formed.

* Different molecular geometries: The atoms in these molecules can arrange themselves in different geometric configurations (e.g., linear, bent, trigonal planar, tetrahedral), further diversifying the possible compounds.

* Different numbers of atoms: The number of nitrogen and oxygen atoms in a compound can vary, leading to a range of molecular formulas. For example, there are oxides of nitrogen like N2O (nitrous oxide), NO (nitric oxide), NO2 (nitrogen dioxide), and N2O4 (dinitrogen tetroxide).

* Presence of other elements: In addition to nitrogen and oxygen, compounds can also include other elements, further expanding the possibilities. For example, nitrous acid (HNO2) and nitric acid (HNO3) contain hydrogen as well.

Examples of nitrogen-oxygen compounds:

* Nitrogen oxides: N2O, NO, NO2, N2O4, N2O5

* Nitric acid: HNO3

* Nitrous acid: HNO2

* Nitrogen dioxide: NO2

* Nitrous oxide: N2O

The combination of these factors leads to a diverse array of nitrogen-oxygen compounds with varying properties and applications.