Chemistry Electrochemistry MDCAT 2017
PMDC Verified Question 59 of 73
In \( NO_3^- \), the oxidation number of "N" is:
A
+5
B
+3
C
+2
D
-3
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: +5
Concept:

The sum of the oxidation states of all atoms in a polyatomic ion must equal the net charge of the ion.

Formula:

$$x + 3(-2) = -1$$

Solution:

  • Let \( x \) be the oxidation state of Nitrogen (N).


  • The oxidation state of Oxygen (O) is generally \( -2 \).


  • Set up the algebraic equation: \( x + 3(-2) = -1 \).


  • Solve for \( x \): \( x - 6 = -1 \implies x = +5 \).


Why other options are incorrect:

A value of \( -3 \) would apply to Ammonia (\( NH_3 \)), not Nitrate. Values of \( +3 \) or \( +2 \) correspond to nitrites or nitrogen monoxide, respectively.

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