• # question_answer Among $A{{l}_{2}}{{O}_{3}},Si{{O}_{2}},{{P}_{2}}{{O}_{3}}$ and $S{{O}_{2}}$the correct order of acid strength is [AIEEE 2004] 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) $A{{l}_{2}}{{O}_{3}}<Si{{O}_{2}}<{{P}_{2}}{{O}_{3}}<S{{O}_{2}}$

Correct Answer: D

Solution :

With decrease in size from Al to S the basic nature of oxide decrease and acidic nature increases. $A{{l}_{2}}{{O}_{3}}<Si{{O}_{2}}<{{P}_{2}}{{O}_{3}}<S{{O}_{2}}$ $A{{l}_{2}}{{O}_{3}}$ is amphoteric, $Si{{O}_{2}}$ is slightly acidic whereas ${{P}_{2}}{{O}_{3}}$ and $S{{O}_{2}}$ are the anhydrides of acids ${{H}_{3}}P{{O}_{3}}$ and ${{H}_{2}}S{{O}_{3}}$.

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