Question

Among \[{{P}_{2}}{{O}_{5}}\] ​,\[A{{s}_{2}}{{O}_{3}}\],\[S{{b}_{2}}{{O}_{3}}\] ​ and \[B{{i}_{2}}{{O}_{3}}\] ​, the most acidic oxide is
A.\[{{P}_{2}}{{O}_{5}}\]
B.\[A{{s}_{2}}{{O}_{3}}\]
C.\[S{{b}_{2}}{{O}_{3}}\]
D.\[B{{i}_{2}}{{O}_{3}}\]

Answer 1

Hint: The compounds can be distinguished on the basis of the element which differs in all these given compounds, in other words all these compounds are oxide of some element. They can be distinguished on the basis of their position in the periodic table.
-As we go down a group, the acidic character decreases as their ionisation enthalpy decreases, because of the bigger size and acids are those which have the ability to accept electrons.

Complete step by step answer:
Generally, the electropositive character of the central atom of the oxide would be the one to determine whether the oxide will be basic or acidic. With increase in electropositive character of the central atom the basic character of the oxide also increases. Similarly, with increase in electronegative character of the central atom, acidic character of the oxide also increases. Across the periodic table from right to left, the electropositive character increases and the electropositive character also increases down the column.
Many of the covalent oxides of the very acidic cations exhibit acidic properties.

Many of these oxides which are acidic in nature dissolve in water in order to give the oxo anion in which the element contains the same oxidation number as that contained by the oxide. The oxide will be soluble in nature if its reaction with water produces a very strong or strong acid as these acids present in the Solution will ionize completely which will shift the equilibrium toward disSolution. If the reaction along with water produces a reasonably acidic oxoacid, the solubility of the oxide is not certain. If the nature of oxoacid which is generated is weakly acidic, the oxide is generally but not always insoluble in water.

So if we consider the question, the compounds given in the question are \[{{P}_{2}}{{O}_{5}}\] ​,\[A{{s}_{2}}{{O}_{3}}\],\[S{{b}_{2}}{{O}_{3}}\] ​ and \[B{{i}_{2}}{{O}_{3}}\] from which we have to justify which one is the most acidic oxide.

As we know that when we move down the group, the atomic size of the elements increases, and the electronegativity of an element decreases, metallic character as well as the electron gain enthalpy increases so acidic character decreases down the group. And we know that all of these elements mentioned in the question belong to the same group, in the order phosphorus, arsenic, antimony and bismuth, down the group.
So \[{{P}_{2}}{{O}_{5}}\] ​ is the most acidic oxide, among all the given options.

Hence the correct option is A.

Note: When we move down the group, the ability of an element to release its electrons which are present in the outermost shell, becomes easier as the effective nuclear charge experienced by the outermost electrons is less.
-That results in decrease of the ionisation enthalpy, and increase of metallic character, hence the acidic character.