Question

Assertion
Nitric oxide is paramagnetic while \[{{\text{N}}_{\text{2}}}{\text{O}}\] is diamagnetic.
Reason
Nitrogen exhibits variable valency in \[{\text{NO}}\] and \[{{\text{N}}_{\text{2}}}{\text{O}}\].
A) Both assertion and reason are CORRECT and reason is the CORRECT explanation of the assertion.
B) Both assertion and reason are CORRECT, but reason is NOT THE CORRECT explanation of the assertion.
C) Assertion is CORRECT, but reason is INCORRECT.
D) Assertion is INCORRECT, but the reason is CORRECT.

Answer 1

Hint: Paramagnetic and diamagnetic behaviour is based on the number of unpaired electrons in the outermost shell of an element or compound. The compound shows paramagnetic behaviour if there are unpaired electrons in it.

Complete step by step answer:
Paramagnetism is the property by which an element shows magnetic behaviour when placed in a magnetic field because of the presence of unpaired electrons and diamagnetism is the property exhibited by an element as it doesn’t show any magnetic behaviour when placed in an external magnetic field.
Here we have nitrogen and oxygen as the elements. Nitrogen has seven electrons and oxygen has eight electrons. So the total number of electrons present in the molecular orbital of \[{\text{NO}}\] will be 15. As the total number of electrons is an odd number, there will be presence of unpaired electrons and the compound will show paramagnetic behaviour.
In \[{{\text{N}}_{\text{2}}}{\text{O}}\], the total number of electrons will be;
\[{{7 \times 2 + 8 = 22}}\]
Here, the number of electrons is an even number and there will not be any unpaired electrons. So, the compound shows diamagnetic behaviour.
But in both these compounds, oxygen shows the same valency but nitrogen exhibits variable valency.
Therefore, we came to know that nitric oxide is paramagnetic and \[{{\text{N}}_{\text{2}}}{\text{O}}\] is diamagnetic and nitrogen shows the different valencies in both of these compounds.

So, option B is correct.

Additional Information:
Paramagnetic elements show magnetic behaviour only at the presence of a magnetic field and they are only weakly attracted by it. There are some elements which are called to be ferromagnetic, who have the ability to retain the magnetic behaviour even after removing the field.

Note: The easy way to identify whether an element is paramagnetic or it is diamagnetic is to look at the number of electrons. Presence of unpaired electrons makes it paramagnetic and absence of unpaired electrons make it diamagnetic.