Oxidation state change in nitrification

Steps:

• In NH₄⁺, oxidation number of N is x + 4(+1) = +1, so x = -3.
• In NO₃⁻, oxidation number of N is x + 3(-2) = -1, so x = +5.
• Change is +5 - (-3) = +8.

Why C is correct:

• +8 matches the difference in oxidation numbers using standard rules where H is +1 and O is -2 in ions.

Why the others are wrong:

• A: –6 reverses the process direction.
• B: +6 undercounts the oxygen influence.
• D: +9 overestimates the final state.

Final answer: C