What is the oxidation number of N in NCl3?

Step by step;

1. 1) Evaluate the oxidation number for other elements/element; In
   this case #Cl#

#Cl ^-# The charge on its ion is -1 #=># that oxidation no. is -1

2) Set up an equation;

We find that the total charge on the compound is 0 ie. it is neutral
So use this formula;

#(n_a)(c _ a ) + (n_b )(c _b) =# Total charge on the compound

Where c represents charge or oxidation number .n represents the number of atoms of that species present in the given compound

Disclaimer ; Charge and oxidation number are not exactly one another.But for sake of simplicity using them as one another

3) solve the equation

#1(c) + 3(-1) = 0#
#1(c) -3 = 0#
#1(c) =3 #
#=>(c) =3#

#therefore# the oxidation number of N is +3..

#"NCl"_3"#

The sum of oxidation numbers in a neutral compound must equal zero.

The oxidation number of group 17/VIIA elements is usually #-1#. Since there are three chlorine atoms in the compound, the total oxidation number for chlorine is #-3#. Since the sum of the oxidation numbers must equal #0#, the oxidation number of nitrogen in the compound is #+3#.

#1(+3) + 3(-1)=#

#(+3)+(-3)=0#