Question

The correct order of decreasing acid strength of oxy-acids of group 15 elements is

• A. HNO$_3$, H$_3$SbO$_4$, H$_3$AsO$_4$, H$_3$PO$_4$
• B. H$_3$PO$_4$, H$_3$AsO$_4$, H$_3$SbO$_4$, HNO$_3$
• C. HNO$_3$, H$_3$PO$_4$, H$_3$AsO$_4$, H$_3$SbO$_4$
• D. HNO$_3$, H$_3$PO$_4$, H$_3$AsO$_4$, H$_3$SbO$_4$

Hint:

For oxy-acids with the same structure, \textbf{acid strength decreases down a group} as electronegativity decreases.

Answer 1

The Correct Option is C

Step 1: Recall that the strength of oxy-acids depends on the electronegativity of the central atom and its ability to stabilize the conjugate base.
Step 2: In group 15, electronegativity decreases down the group: \[ \text{N}>\text{P}>\text{As}>\text{Sb} \]
Step 3: Higher electronegativity of the central atom increases the acidic strength of the oxy-acid.
Step 4: Therefore, the decreasing order of acidic strength is: \[ \text{HNO}_3>\text{H}_3\text{PO}_4>\text{H}_3\text{AsO}_4>\text{H}_3\text{SbO}_4 \]
Step 5: Hence, option (C) is correct.