Question

Which of the following oxide is most acidic?
A. $N{a_2}O$
B. MgO
C. $Si{O_2}$
D. $C{l_2}{O_7}$

Answer 1

Hint: To solve this question, we need to understand the concept of acidic oxides. Acidic oxide which is also known as acid anhydride. They are oxides that react with water to form an acid, or with a base to form a salt. They are oxides of either nonmetals or of metals in high oxidation states. Their chemistry can be systematically understood by taking an oxoacid and removing water from it, until only an oxide remains.

Complete answer:
We know that an acidic oxide is formed when combined with water to form an acid. Also, the oxides of non-metals are acidic in nature.
$C{O_2}(g) + {H_2}O(l) \to {H_2}C{O_3}(aq)$
Based on this property of acidic oxide $Si{O_2}$ , $N{a_2}O$ and MgO are known to be basic oxides. Whereas we know that non-metallic oxides are acidic. So, $C{l_2}{O_7}$ has the highest acidity because it is an oxide of non-metal. Therefore, the option D is correct.
We also know that, when $N{a_2}O$ reacts with water it forms sodium hydroxide NaOH which turns the red litmus paper blue. So, $N{a_2}O$ is said to be a basic oxide. Whereas $C{l_2}{O_7}$ reacts with water and forms perchloric acid i.e. $HCl{O_4}$ that turns the blue litmus paper red. Therefore, $C{l_2}{O_7}$ is an acidic oxide.
Therefore option D is correct.

Note:
In case of metals, as we move down the group metallic character increases and the basic nature increases. Hence, most acidic will be BeO as Be is the least metallic in group 2 elements. Therefore, BeO is the most acidic in nature as the acidity of oxides decreases with an increase in the electropositive character of the central atom.