Let the oxidation state of nitrogen in the given compounds be x.
(a) N2H4x+1 : 2x+(+1)4=0 2x=−4 x=−2
(b) NH3x+1 : x+(+1)3=0 x=−3
(c) N3Hx+1 : 3x+(+1)=0 3x=−1 x=−1/3
(d) NH2OHx+1−2+1 : x+(+1)2+(−2)+(+1)=0 x+2−2+1=0 x+1=0 x=−1
The oxidation state of nitrogen is highest in N3H.
i.e. in minus, −31 is greater than −3.