Question

Which of the following is the most basic oxide?
(A) $S{b_2}{O_3}$
(B) $B{i_2}{O_3}$
(C) $Se{O_2}$
(D) $A{l_2}{O_3}$

Answer 1

Generally metal reacts with oxygen to give basic compounds of oxygen or basic oxide. We know the basicity of an oxide depends on the electropositive character of the central metal atom. Also as we move from top to bottom of the periodic table the electropositive character of an element increases which means basicity also increases.

Complete Step by Step Solution:
Oxides are binary compounds produced by the reaction of oxygen with metals and non-metals. We can classify oxides into three main categories: acidic, basic, and amphoteric respectively based on their acid-base properties.

Generally, acidic oxides produce acidic solutions with water and basic oxides produce basic solutions with water. Amphoteric oxides react either with acid as well as a base to form salt and water. As we move from left to right in the periodic table, the non-metallic character of an element increases, and thereby acidity of an oxide increases but the metallic character decreases, and thereby basicity of an oxide decreases. Whenever we move from top to bottom in the periodic table, the non-metallic character decreases and the metallic character or electropositive character increases.

Now both $S{{b}_{2}}{{O}_{3}}$ and $A{{l}_{2}}{{O}_{3}}$ are amphoteric oxides since they can act either as acid or as a base to form salt and water.

$Se$ in $Se{{O}_{2}}$ belongs to group 16, having an oxidation state $(+4)$ and $Se$ is non-metal, and forms acidic oxide $Se{{O}_{2}}$. The oxidation state of metal in metallic oxide decreases, thereby increasing its basic nature. $Bi$in $B{{i}_{2}}{{O}_{3}}$ belongs to group 15, having an oxidation state $(+3)$. Therefore $B{{i}_{2}}{{O}_{3}}$ is the most basic oxide, and the metallic character of $Bi$ increases as we go down the group.
Thus, the correct answer is (B).

Note: Metal oxides are basic because they react with dilute acids to form salts and water. Since the oxides of groups one and two are strongly alkaline in nature, group one is called an alkali metal and group two is called an alkaline earth metal.