For most compounds in which a nitrogen atom bears no formal charge, the valence of this nitrogen atom is

3

Explanation:

Hello,

In this case, as nitrogen is not bearing any formal charge, we apply its mathematical definition to find such oxidation state:

Formal charge= # of valence electrons - # of lone-pair electrons - 1/2 # of bond pair electrons

Since no formal charge is born, no lone-pair electrons are formed and 6 bond pair electrons are always present for the nitrogen to complete the octate, the valence turns out into:

# of valence electrons = 0 + 0 + 1/2 * 6

# of valence electrons = 3

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