* Ammonia (NH₃): The most common compound formed by hydrogen and nitrogen is ammonia.

* Formula: The chemical formula for ammonia is NH₃. This means there are 3 hydrogen atoms for every 1 nitrogen atom.

Therefore, the ratio of hydrogen atoms to nitrogen atoms in ammonia is 3:1.

It seems there might be a typo in the options provided. The correct ratio is 3:1, not 2:1.