As per oxidation state rules, the most electronegative element will have a negative oxidation state and the other element will have a positive oxidation state.
N is more electronative than H, so H will have a positive oxidation state and nitrogen will have a negative oxidation state.
You can also use the rule that states the hydrogen mostly has 1+ oxidation state,except when it is bonded to metals.
In conclusion the oxidation state of H in NH4 (1+) is 1+.
Now you must know that the sum of the oxidations states equals the charge of the ion, which in this case is 1+.
That implies that 4* (1+) + x = 1+
=> x = (1+) - 4(+) = 3-
Answer: the oxidation state of N is 3-, that is the option b.
The sum of the masses of potassium and iodine equals the mass of the product, potassium iodide. The results are consistent with he law of conservation of mass.
