Question

Assertion:
Aluminium and gallium are trivalent in their compounds but monovalent compounds are the most stable down the ${13^{th}}$ group.
Reason:
Down the group$\left( {{{13}^{th}}} \right)$, the stability of $+ 3$ state decreases and that of $+ 1$ state increases due to the prominent “inert pair” effect.
A.Both the assertion and reason are correct and reason is the correct explanation for assertion.
B.Both the assertion and reason are correct and reason is not the correct explanation for assertion.
C.Assertion is incorrect but reason is incorrect.
D.Both Assertion and reason are incorrect.

Answer 1

We know the non-participation of the 2 s electrons in bonding thanks to the high energy required for unpairing them. This is called an inert pair effect which was planned by Sidgwick.
Examples of Inert combine Effect: The inert pair result among cluster four and group five elements. $S{n^{2 + }}$and $P{b^{2 + }}$ and $S{b^{3 + }}$and $B{i^{3 + }}$ That are the lower oxidation numbers of the weather are shaped thanks to the inert pair effect. Once the s electrons stay paired the oxidation state is less than the characteristic oxidation state of the group.

Complete step by step answer:
We have to remember that the general oxidation state exhibited by the group 13 elements in the group are +3 and +1.
We know that, down the group $\left( {{{13}^{th}}} \right)$ the stability of $+ 3$ state decreases and that of $+ 1$ state increases due to the prominent "inert pair" effect.
$A{l^{3 + }} > G{a^{3 + }} > I{n^{3 + }} > T{l^{3 + }}$
$T{l^ + } > I{n^ + } > G{a^ + } > A{l^ + }$
The inert s-pair effect is significant in the group $\left( {{{13}^{th}}} \right)$ elements. It results in a variety of oxidation states. In lighter elements $+ 3$states is the most stable but $+ 1$ state increases with atomic number. This inert pair effect is highest in thallium.

So, the correct answer is Option A.

Additional Information:
We know, Covalency is defined because the number of electrons present within the outermost shell which is shared by an atom during a compound. The atoms are inert if the atom has filled electron configuration. If the outermost shell isn't filled then to fill the outermost shell, it accepts or donates electrons between other atoms. The valency of an atom is the number of electrons present within the outermost shell. If the electrons are shared between covalent compounds then it's termed as covalency.
For Example, the amount of valence electrons in carbon is four and it needs four more electrons to possess filled outermost electrons and hydrogen has one electron in its valence shell as a result carbon shares its electrons with four hydrogen atoms. Thus the covalency of carbon is four.

Note: As we know that the number of valence electrons in oxygen is six and it needs two electrons to possess a filled configuration. Thus, the covalency of oxygen is 2 because it forms a covalent bond and the number of valence electrons in nitrogen is five and it needs three electrons to possess a filled configuration that of nitrogen is three because it forms a triple bond.
We must remember that the covalency and electrovalency are different from one another. If the donation or acceptance of electrons occurs in an ionic compound then it's called electrovalency while the electrons are shared between covalent compounds is known as covalency.