Question

Most acidic oxide among the following is?

• A. ${\mathrm{NO}}_2$
• B. ${\mathrm{P}}_2{\mathrm{O}}_5$
• C. ${\mathrm{Cl}}_2{\mathrm{O}}_7$
• D. ${\mathrm{Cl}}_2\mathrm{O}$

Answer 1

The correct option is C

${\mathrm{Cl}}_2{\mathrm{O}}_7$

Explanation for correct option:

Option (c) ${\mathrm{Cl}}_2{\mathrm{O}}_7$

• The covalent character determines the acidic nature.
• The higher the covalent character, the more acidic the oxides, and covalent character is determined by the element's oxidation state.
• Because Chlorine atom ($\mathrm{Cl}$) possesses a $+7$ oxidation state in Chlorine heptoxide i.e., ${\mathrm{Cl}}_2{\mathrm{O}}_7$.
• It has the most polarising power and covalent nature, making ${\mathrm{Cl}}_2{\mathrm{O}}_7$ the most covalent, and hence the most acidic oxide.
• Also, when ${\mathrm{Cl}}_2{\mathrm{O}}_7$ reacts with water, ${\mathrm{HClO}}_4$ forms, which is the strongest acid.
• Therefore, ${\mathrm{Cl}}_2{\mathrm{O}}_7$ is acidic.

Explanation for incorrect options:

Option (a) ${\mathrm{NO}}_2$

Nitrogen dioxide (${\mathrm{NO}}_2$) is an acidic oxide, which quickly interacts with water (${\mathrm{H}}_2\mathrm{O}$) to form an acidic solution of Nitric acid (${\mathrm{HNO}}_3$) and Nitrogen Monoxide ($\mathrm{NO}$).

Option (b) ${\mathrm{P}}_2{\mathrm{O}}_5$

Because it is an anhydride of Phosphoric acid, Phosphorus Pentoxide (${\mathrm{P}}_2{\mathrm{O}}_5$) is used as a desiccating and drying agent.

Option (d) ${\mathrm{Cl}}_2\mathrm{O}$

Chlorine dioxide is a neutral oxide in nature. So this option is incorrect.

Hence, ${\mathrm{Cl}}_2{\mathrm{O}}_7$ is the most acidic among the given oxides.