Question

Which of following is more acidic in its following aqueous
A. ${H_2}O$
B. ${H_2}S$
C.${H_2}Se$
D.${H_2}Te$.

Answer 1

Acid strength measures the ability of the acid to lose its H+ ion. Higher the ${H^ + }$ ion loss in aqueous solution higher will be acidic strength. A strong acid completely ionizes in a solution whereas a weak acid only partially ionizes.

Complete answer:
The strength of an acid depends on the following two factors.
Strength of $H - A$ bond
Polarity of $H - A$ bond
In general if the strength of $H - A$ bond is weaker, the acid will be stronger . Similarly, if the polarity of $H - A$ bond is greater, stronger is the acid. These two factors make the dissociation of acid molecules into ${H^ + }$ and $A$- easier results in the increase in the acidity.
As the atom becomes larger, the bond gets weaker. Consequently, acid strength increases therefore the atomic size of $A$ also affects the acid strength.
So in option no (A) ${H_2}O$ will be least acidic because H-A bond is stronger in H2O also atomic size of Oxygen atom is least in its group therefore bond will be stronger and it will be least acid.
Similarly $Te$ is the largest atom in the above option. So $Te$ will have the weakest H-A bond and strongest acidic character. Also the polarity of $Te$is greatest among options.
So the correct option is option D.

Note: However, bond strength is a more determining factor when we consider and compare acid strengths of elements in the same group of the periodic table, using the above two factors.