Question

Oxidation of nitrites in presence of permanganate of potash leads to formation of:

Answer 1

Oxidation is the loss of electrons during a reaction by a molecule, atom or ion. Oxidation occurs when the oxidation number of a molecule, atom or ion is increased. The other process is named reduction, which occurs when there's a gain of electrons or the oxidation number of an atom, molecule, or ion decreases.

Complete answer:
Oxidation of nitrites is in the presence of the permanganate of the potash that leads to the formation of the nitrates ($NO_{3}^-$). Permanganate of potash is the good oxidant so oxidation number of N is increased from nitrites-3 to nitrate-5.
Ammonia oxidation is the fundamental core which processes within the global biogeochemical organic process. Oxidation of the ammonia ($NH_3$) to nitrite ($NO_{2}^−$) is the first and rate-limiting step in the nitrification and of this is administered by the distinct groups of microorganisms.
When the nitrates are produced then, ammonia and the nitrite levels become zero, your tank is fully cycled and your biological filter is fully functioning (from 2-6 weeks). In low levels, nitrates aren't highly toxic to fish. Routine partial water changes of about 10% should keep nitrate levels within a secure range.

Note:
Nitro somonas bacteria primarily change nitrogen gas to nitrite and later Nitrobacter converts nitrite to nitrate, a plant nutrient. Plants absorb ammonium and nitrate during the assimilation process, after which they're converted into nitrogen-containing organic molecules, like amino acids and DNA.