Question

What is the main reason of diagonal relationship between lithium and magnesium
A. Electronegativity remains constant the same on moving parallel.
B. Electronegativity remains constant the same when moving horizontally.
C. Electronegativity remains constant the same on moving diagonally.
D. Electronegativity remains constant the same when moving vertically.

Answer 1

Hint- In order to deal with this question first we will define the term diagonal relationship then further we will take an example of pair lithium and magnesium to get the required reason.

Complete step-by-step answer:
In the second and third cycles (first 20 elements) of the periodic table, a diagonal connection is said to occur for such pairs of diagonally adjacent elements. Both pairs (lithium $\left( {Li} \right)$ and magnesium $\left( {Mg} \right)$ , beryllium $\left( {Be} \right)$ and aluminum $\left( {Al} \right)$ , boron $\left( B \right)$ and silicon $\left( {Si} \right)$ , etc.) show identical properties; boron and silicon, for example, are also semiconductors, producing hydrolyzed halides in water with acidic oxides
So, Lithium and magnesium show diagonal relationship as they have the same polarizing power so elements of the second period show similarities with elements of the third period of the next group.
Properties which show similarities in lithium and magnesium are:
Both compounds lithium and magnesium form oxides $LiOH$ and $Mg{\left( {OH} \right)_2}$ both are weak bases while hydroxides of other members of their group form strong bases.
The carbonates and hydroxides and also nitrates of both lithium and magnesium decompose on heating.
Due to the small size of $\left( {Li} \right)$ and $\left( {Mg} \right)$ their halides are soluble in organic solvents.
They form hydrates like $LiCl.{H_2}O$ and $MgC{l_2}.2{H_2}O$.
The diagonally opposite elements possess almost similar electronegativities and therefore almost similar electropositive character.
Hence, the main reason of diagonal relationship between lithium and magnesium electronegativity remains constant the same on moving diagonally.
So, the correct answer is option C.

Note- Electronegativity is a function of an atom's ability to draw electrons from a bonding pair. The most widely used is the Pauling scale. A value of 4.0 is given to fluorine (the most electronegative element), and values vary down to cesium and francium which are the least electronegative at 0.7.