For HNO3:
Let oxidation state of N=x
1+x+3(−2)=0
⇒x=+5
For NO:
Let oxidation state of N = x
x+(−2)=0
⇒x=+2
For N2:
Let oxidation state of N = x
x=0
For NH4Cl:
Let oxidation state of N = x
4(1)+x+(−1)=0
⇒x=−3
H+5NO3,+2NO,0N2,−3NH4Cl
Hence, option (b) is correct.