Some bacteria like <em><u>rhizobium</u></em> and <u><em>blue green algae</em></u> are able to fix nitrogen gas from the atmosphere to enrich the soil with nitrogen compounds and increase its fertility. The nitrogen-fixing bacteria and blue green algae are called <u><em>biological nitrogen fixers.</em></u>
The atoms of the solid have to form a crystalline structure, which means that they have an ordered configuration that is the same throughout the entire solid.
