Fungi and bacteria release nitrogen stored in dead tissue through a decomposition process called:
a. nitrogen fixation.
b. ammonification.
c. denitrification.
d. nitrification

Nitrification is an aerobic process performed by nitrifying bacteria or archaea which transform ammonia into nitrite (NO2-) and then the nitrite to nitrate (NO3−). Nitrates are inorganic forms of nitrogen that plants can use as a nitrogen source so, the nitrification is an important step in the nitrogen cycle in soil.    

(NH4+ → NO2− → NO3−)

Explanation:

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the answer is na (sodium)