In NH4OH, the oxidation number of nitrogen can be determined by considering the oxidation numbers of the other elements in the compound. The oxidation number of hydrogen H is +1, and there are four hydrogen atoms in the ammonium ion NH4+ , so the total oxidation number for hydrogen is +4. The oxidation number of oxygen O is -2, and there is only one oxygen atom in the hydroxide ion OH- , so the total oxidation number for oxygen is -2.Now, let's denote the oxidation number of nitrogen N as x. According to the oxidation number rules, the sum of the oxidation numbers in a neutral compound should be equal to zero. So, we can set up the following equation:x + 4 +1 + -2 = 0Solving for x:x + 4 - 2 = 0x + 2 = 0x = -2Therefore, the oxidation number of nitrogen N in NH4OH is -2.