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Diagonal relationship is not shown by:
A. $\text{Li and Mg}$
B. $\text{Be and Al}$
C. $\text{B and Si}$
D. $\text{C and P}$

Last updated date: 13th Jun 2024
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Hint: A diagonal relationship exists between some pairs of elements which are diagonally adjacent and they are present in the second and third periods of the periodic table. Factors are the polarizing power which depends on ionic radius being almost similar to the diagonally placed elements because of which such relationships occur.

Complete answer:
First, let us know the reason of diagonal relationship; on crossing a period of the periodic table, the size of the atom decreases and on descending a group the size of the atom increases and other Let us now see the similarities in properties of the elements as outcome of diagonal relationship. Let us study the examples one by one.
A.$\text{Li and Mg}$:

S. NoType of propertiesSIMILARITIES shown by Magnesium and Lithium
1Reaction with waterReact slowly with water and are less soluble. Hydroxides decompose on heating.
2Reaction with nitrogenFormation of nitrides takes place by direct combination of elements with nitrogen, $\text{M}{{\text{g}}_{3}}{{\text{N}}_{2}}\text{ and L}{{\text{i}}_{3}}\text{N}$.
3Carbonate and hydrogen carbonatesCarbonates decompose in heating to oxides and$\text{C}{{\text{O}}_{2}}$. Solid hydrogen carbonates are not formed.
4HydratesChlorides are deliquescent and crystallise from aqueous solution as hydrates, $\text{LiCl and MgC}{{\text{l}}_{2}}$.

B.$\text{Be and Al}$:
S. No.Type of propertiesSIMILARITIES shown by Aluminium and Beryllium
1Not easily attacked by acidsDue to the presence of an oxide film on the surface of the metals, they are not easily attacked by acids.
2Reaction with alkaliReacts with excess of alkali to give beryllate and aluminate ions, ${{\left[ \text{Be}{{\left( \text{OH} \right)}_{4}} \right]}^{2-}}\text{and }{{\left[ \text{Al}{{\left( \text{OH} \right)}_{4}} \right]}^{-}}$.
3Lewis acidsThe chlorides of both are soluble in organic solvents and are strong Lewis acids as they are electron deficient. Also used as Friedel craft catalysts.
4Complex FormationBoth the ions have the tendency to form strong complexes like$\text{BeF}_{4}^{2-}\text{ and AlF}_{6}^{3-}$.

C.$\text{B and Si}$:
S. NoType of propertiesSIMILARITIES shown by Boron and Silicon
1Exhibit property of non-metalsAre high melting and boiling point.
2Different solid formsExist in crystalline and amorphous forms.
3Conduction of electronsNon- conductors of electricity and semiconductors also.
4Ability to release${{\text{H}}^{+}}$ionAre very weak acids, ${{\text{H}}_{3}}\text{B}{{\text{O}}_{3}}\text{ and }{{\text{H}}_{4}}\text{Si}{{\text{O}}_{4}}$.
5Hydrolysis of chloridesThe reaction of hydrolysis is $\begin{align} & \text{BC}{{\text{l}}_{3}}+3{{\text{H}}_{2}}\text{O}\to \text{B}{{\left( \text{OH} \right)}_{3}}+3\text{HCl} \\ & \text{SiC}{{\text{l}}_{4}}+3{{\text{H}}_{2}}\text{O}\to \text{Si}{{\left( \text{OH} \right)}_{4}}+4\text{HCl} \\ \end{align}$

D. C and P: Shows no similar properties.
So, the correct answer is “Option D”.

Note: The elements may be present in different groups and periods, but still resembles each other, due to small size. So, the resemblance occurs by size similarity not by just being present in the same group. Like, Li shows similarities with Mg but shows distinction in some properties with its own group (I).