Question

Among $Al _{2} O _{3}, SiO _{2}, P _{2} O _{3}$ and $SO _{2}$ the correct order of acid strength is

• A. $SO _{2}< P _{2} O _{3}< SiO _{2}< Al _{2} O _{3}$
• B. $SiO _{2}< SO _{2}< Al _{2} O _{3}< P _{2} O _{3}$
• C. $Al _{2} O _{3}< SiO _{2}< SO _{2}< P _{2} O _{3}$
• D. $Al _{2} O _{3}< SiO _{2}< P _{2} O _{3}< SO _{2}$

Answer 1

Answer: (D)

Acidity of the oxides of non metals increases with the electronegativity and oxidation number of the element.

$Al _{2} O _{3}< SiO _{2}< P _{2} O _{3}< SO _{2}$

$Al _{2} O _{3}$ is amphoteric. $SiO _{2}$ is slightly acidic whereas $P _{2} O _{3}$

and $SO _{2}$ are the anhydrides of the acids $H _{3} PO _{3}$ and $H _{2} SO _{3}$