[kstervic]

Hi I am having some trouble with one particular question.
The question is: What is the oxidation number for the atom N is KNO₂?
This is the explanation I got.

It looks like we have 2 unknown oxidation numbers (K & N), but the truth is that there is only one unknown (N).  This is because KNO2 is a polyatomic (because it is called potassium nitrite, & nitrite is a polyatomic ion).  Since polyatomic molecules are ionic, this means we know that the oxidation number of K must be +1 by the uncriss-crossing rule.  We then look at O & its oxidation number is -2.  The molecule is neutral, so the algebraic expression equals 0.  We then solve as usual.


I understand every line of that explanation except how we find the oxidation number of K.
How do we use the uncriss-crossing rule to find that K has a charge of +1?
Thank you in advance!

[Borek]

One of the basic rules when assigning oxidation numbers is that alkali metals (Li, Na, K, Rb, Cs) are always +1.

What they probably mean is that NO₂^- is known to be -1 as a group, so potassium must be K⁺ (or +1).

[Partha Sarker]

 It will be +3