Question

Which of the following is the correct order of gradually decreasing basic nature of the oxides?
(A) \[A{l_2}{O_3},MgO,C{l_2}{0_7},SO_3^{}\]
(B) \[C{l_2}{O_7},S{O_3},A{l_2}{0_3},MgO\]
(C) \[S{O_3},C{l_2}{0_7},MgO,A{l_2}{O_3}\]
(D) \[MgO,A{l_2}{O_3},S{O_3},C{l_2}{O_7}\]

Answer 1

Hint: Oxides can be classified as acidic oxides, basic oxides and neutral oxides. Those oxides that react with water to form bases are called basic oxides. Some oxides are both basic as well as acidic in nature. They are called amphoteric oxides. Metals form basic oxides. Thus, more is the metallic character; more is the basic nature of oxides. Also, more is the non- metallic character, more is the acidic nature of oxides.

Complete Step by Step Solution:
\[A{l_2}{O_3}\]is an amphoteric oxide. The metal in this oxide is\[A{l^{ + 3}}\]. \[A{l_2}{O_3}\] reacts with water to form\[Al{\left( {OH} \right)_3}\].
\[MgO\]is a basic oxide with \[M{g^{ + 2}}\]metal. \[MgO\] reacts with water to form magnesium hydroxide $Mg{(OH)_2}$.

\[C{l_2}{0_7}\]and \[S{O_3}\]are acidic oxides as they involve non-metals \[Cl\]and \[S\]respectively. \[C{l_2}{0_7}\] reacts with water to form\[HCl{0_7}\]. \[S{O_3}\] reacts with water to form\[{H_2}S{O_4}\]. Thus, they have a tendency to react with water to form two well-known acids. Hence these two have the least basic nature.

Magnesium is more metallic in nature as compared to aluminium because on moving from left to right in a period, electronegativity increases so it is more difficult to lose electrons and thus, metallic nature decreases.

Thus, the order of basic oxides in decreasing order is\[MgO,A{l_2}{O_3},S{O_3},C{l_2}{O_7}\.

Note: If the amphoteric oxides are stated to be basic oxides as given in the question then it is to be noted that it is the basic nature of oxides that is to be considered and acidic nature of oxides is ignored for the time being.