State the oxidation number assigned to each bold element in the formula: nh4+1 a 3 b -3 c -1 d 6

The fomula is NH4 (1+)

There are only two elements N and H.

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-

  the oxidation state of N is 3-, that is the option b.