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Which of the following acids is most acidic?
A. BaO
B. MgO
C. Cao
D. BeO

Answer Verified Verified
Hint: In metals moving down the group metallic character increases, so basic nature increases and Be is the least metallic in group 2 elements.

Complete answer:
Use Fajan rule in this case
We can see the charge on cation and anion are the same so it all depends on the size of the cation.
According to Fajan rule as the size of the cation increases the polarizing power decreases and the covalent character decreases or the ionic character increases. Hence basic character increases down the group.
Ba is a large cation so the polarising power is less and hence this will not be the correct option.
Mg is metal and we all know that metal oxides are basic so MgO will not be the correct answer
Ca is a large cation so the polarising power is less and oxides Ca is not much acidic so this will also not be the correct option.
Be is a small cation so the polarising power is high and it forms most acidic oxides and it has the most covalent. So Beo is the most acidic

Hence the correct option is (D) BeO.

Note: Students can make confusion in determining acidic and basic character by using the Fajan rule, make sure to remember that as we go down the group basic character increases and acidic character decreases. therefore BeO is most acidic from all above acid
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