Question

What is the order of basic nature of hydrides of VA group elements?
A. $As{{H}_{3}}>Sb{{H}_{3}}>P{{H}_{3}}>N{{H}_{3}}$
B. $N{{H}_{3}}>Sb{{H}_{3}}>P{{H}_{3}}>As{{H}_{3}}$
C. $N{{H}_{3}}>P{{H}_{3}}>As{{H}_{3}}>Sb{{H}_{3}}$
D. $P{{H}_{3}}>N{{H}_{3}}>Sb{{H}_{3}}>As{{H}_{3}}$

Answer 1

Hint: The periodic table is designed on the basis of the increasing atomic number such that different groups as well as different periods show a certain order in their properties due to repetitive trends in the periodic table called periodicity.

Complete step by step solution:
-Many types of compound can be used as electrolytes but the most preferred compounds are acids, bases and salts.
-Acids are the compounds that donate ${{H}^{+}}$ ion to become anion. Bases are compounds that accept the ${{H}^{+}}$ ion and convert into cation. Salts are the compounds formed mainly by the reaction of acids and bases.
-The strength of acidic nature is inversely related to the strength of the basic nature of a compound. It means that strong acid has a weak base and vice versa. So we can solve this question in two ways, either by finding the basic strength directly or by inverting the order of the acidic strengths.
-In hydrides, hydrogen atom is linked to the central atom through a covalent bond whose nature decreases down the group due to the increase in the metallic character of the atoms down the group.
-The hydrides of group 15 elements form by connecting 3 hydrogen atoms to the central atom to complete the octet of the elements. Their strength follows a pattern in their strength of covalent bond which is responsible for the basic strength as well.
-The basic strength in a compound depends on the electron density of the compound, size of the compound, electronegativity of the atoms or ions, number of delocalizations possible in the compound, etc.
-As we move down the group, the size of the atoms increases due to the addition of the extra shell. This reduces their electronegativities. The covalent bond nature is highly dependent on this character as it is formed in the atoms with similar electronegativities.
-So the covalent bond strength decreases down the group and the metallic character increases. Thus, the basic strength decreases down the group and can be shown as
$N{{H}_{3}}>P{{H}_{3}}>As{{H}_{3}}>Sb{{H}_{3}}$

Therefore, the correct option is C.

Note: As the size increases, the orbitals of the atoms also increase. The covalent bond depends on the overlapping of the orbitals. The overlapping becomes ineffective as the size increases and so the covalent bond strength decreases resulting in less basic character.