Question

Among $A{l}_2{O}_3,Si{O}_2,P_2{O}_3$ and $S{O}_2$ the correct order of acid strength is:

• A. $A{l}_2{O}_3<Si{O}_2<S{O}_2<P_2{O}_3$
• B. $Si{O}_2<S{O}_2<A{l}_2{O}_3<P_2{O}_3$
• C. $S{O}_2<P_2{O}_3<Si{O}_2<A{l}_2{O}_3$
• D. $A{l}_2{O}_3<Si{O}_2<P_2{O}_3<S{O}_2$

Answer 1

The correct option is D $A{l}_2{O}_3<Si{O}_2<P_2{O}_3<S{O}_2$

As electronegativity difference between element and oxygen decreases the acidic character of oxides increases. The electronegativity also increases with increasing oxidiation state. In general, as non-metallic character increases across the period, the acidic character of their oxides increases.Again the oxides of metalloid are amphoteric and oxides of metal are basic.
$A{l}_2{O}_3$ ​ is amphoteric,$Si{O}_2$ ​ is slightly acidic whereas $P_2{O}_3$ ​ and $S{O}_2$ ​ are anhydrides of acid $H_{3}P{O}_3$ ​ and $H_{2}S{O}_3$ ​ .
So the correct order of acidic strength oxides of 3rd period elements is $A{1}_2{O}_3<Si{O}_2<P_2{O}_3<S{O}_2$ ​