Question

Assertion : Amongst the trihalides of nitrogen, $N{F_3},NC{l_3},NB{r_3}$ and $N{I_3},N{F_3}$ is least basic.
Reason : In $N{F_3}$ , the fluorine has the highest value of electronegativity and thus the lone pair of electrons on atoms is strongly bound.
Read the above assertion and reason and choose the correct option regarding it.
$(a)$ Both assertion and reason are correct and reason is the correct explanation for the assertion.
$(b)$ Both assertion and reason are correct but reason is not the correct explanation for assertion
$(c)$ Assertion is correct but reason is incorrect
$(d)$ Assertion is incorrect but reason is correct.

Answer 1

In these types of questions, our main focus is on assertion and reason. We must focus on assertion and reason statements for choosing the correct options. Because if we cannot relate the assertion and reason we can’t choose the correct option.

Complete answer:
First we need to understand the assertion statement. It says $N{F_3}$ is least basic. The reason is, down the group, the size of the halides increases. So electronegativity or the ability to pull electrons toward itself decreases, this means that tendency to lose electrons increases. Basicity defines how easily it can lose electrons, thus basic characteristics decrease down the group.
Thus, the assertion statement is correct.
Now, we go to the reason part, fluorine compared to other elements is more electronegative because it requires only one electron to complete an octets and attain stability, and the distance at which valence electrons reside is the minimum as compared with other elements because of its smaller size. So the lone pair on the atom is stronger than that any other atom does.
So, the reason part Is also correct.
Option: $(a)$ Both assertion and reason are correct and reason is the correct explanation for the assertion.

Note:
Fluorine is the most electronegative element, still its electron affinity is less than that of chlorine. This happens due to the smaller size of fluorine. All the electrons in the atom repel the incoming electron significantly. We can also understand that due to inert pair effect electronegativity decreases down the group.