Question

converting atmospheric nitrogen into a usable form by bacteria or lightning is known as
nitrogen fixation
denitrification
ammonification
assimilation

Explanation:

Nitrogen fixation is the process where atmospheric nitrogen (\(N_2\)) is converted into ammonia (\(NH_3\)) or other nitrogen - containing compounds that plants can use. Bacteria (such as Rhizobium in root nodules of legumes) and lightning (high - energy conditions in lightning can cause \(N_2\) to react with oxygen to form nitrogen oxides which then can be converted into usable forms) are involved in this conversion. Denitrification is the reduction of nitrates (\(NO_3^-\)) to nitrogen gas (\(N_2\)), ammonification is the conversion of organic nitrogen to ammonia (\(NH_3\)), and assimilation is the uptake of nitrogen compounds by plants.

Answer:

Nitrogen Fixation