Question

Match list I with list II. Choose the correct matching codes from the choices given:

List I	List II
a) $ Be{H_2} $	1. Complex
b) $ As{H_3} $	2. Lewis acid
c) $ {B_2}{H_6} $	3. Interstitial
d) $ La{H_3} $	4. Covalent
e) $ LiAl{H_4} $	5. Intermediate
	6. Ionic

(A) $ a - 6 $ , $ b - 2 $ , $ c - 4 $ , $ d - 5 $ , $ e - 1 $
(B) $ a - 6 $ , $ b - 2 $ , $ c - 4 $ , $ d - 3 $ , $ e - 1 $
(C) $ a - 6 $ , $ b - 4 $ , $ c - 2 $ , $ d - 3 $ , $ e - 5 $
(D) $ a - 6 $ , $ b - 4 $ , $ c - 2 $ , $ d - 3 $ , $ e - 1 $
(E) $ a - 4 $ , $ b - 6 $ , $ c - 2 $ , $ d - 6 $ , $ e - 1 $

Answer 1

Hint: Covalent bonds only form between non-metallic elements because these elements have the same or similar electronegativity values. Ionic compounds are formed from strong electrostatic interactions between ions, which result in higher melting points and electrical conductivity compared to covalent compounds. Covalent compounds have bonds where electrons are shared between atoms.

Complete answer:
A Lewis acid is a chemical species that contains an empty orbital that is capable of accepting an electron pair from a Lewis base to form a Lewis adduct.
These are highly electropositive in nature though the significant covalent character is found in the lighter metal hydrides like Lithium hydride ( $ LiH $ ), Beryllium hydride ( $ Be{H_2} $ ​). $ Be{H_2} $ ​ is polymeric in nature.
According to fajan’s rule, covalent character usually comes from having a cation that is very small reacting with a relatively large anion. Hence the compounds of $ Be $ are large covalent due to extensive polarization. So $ Be{H_2} $ is covalent. Also, we get $ As{H_3} $ ​ is an ionic molecule.
In Lanthanides, the formation of trihydride is associated with an increase in 8–10% volume, and this is linked to greater localization of charge on the hydrogen atoms which become more anionic ( $ H $ − hydride anion) in character.
Hence $ LaH_3 $ is ionic in nature.
 $ {B_2}{H_6} $ ​ is lewis acid because in the structure of diborane two electrons are shared between three centres. So, the boron centres become highly electron-deficient. Also $ LiAl{H_4} $ ​ is a complex Hydride.
Hence the correct option is E. $ a - 4 $ , $ b - 6 $ , $ c - 2 $ , $ d - 6 $ , $ e - 1 $ .

Note:
Covalent compounds or molecular compounds are chemical compounds made of elements connected by covalent bonds. Complex compound is a type of compound formed by the association between a central metal atom along with surrounding non-metal atoms or ions or ligands bonded by covalent, ionic or co-ordinate bonds.
Fajan’s rule is used to predict whether a chemical bond will be covalent or ionic. This depends on the charge and the size of the cations and anions.