Ontario Grade 9 Science Class Practice Exam 2025 – Your Complete Guide to Exam Success!

Nitrification is the process of converting ammonia into nitrites and then into nitrates. This is not the correct answer because it is the conversion of nitrites into nitrates, not the conversion of nitrates into nitrogen gas.

Assimilation is the process of incorporating nitrogen into living organisms through the consumption of nitrogen-containing compounds. This is not the correct answer because it does not involve the conversion of nitrates into nitrogen gas.

Ammonification is the process of converting organic nitrogen into ammonia. While this is a step in the nitrogen cycle, it does not involve the conversion of nitrates into nitrogen gas.

Denitrification is the correct answer because it is the process of converting nitrates into nitrogen gas, which is then released back into the atmosphere. This occurs in anaerobic conditions by denitrifying bacteria.