Question

On combustion of Li, Na and K in excess of air, the major oxides formed, respectively, are

• A. ${\mathrm{Li}}_2{\mathrm{O}}_2,{\mathrm{Na}}_2{\mathrm{O}}_2\mathrm{and}{\mathrm{K}}_2{\mathrm{O}}_2$
• B. ${\mathrm{Li}}_2\mathrm{O},{\mathrm{Na}}_2{\mathrm{O}}_2\mathrm{and}{\mathrm{KO}}_2$
• C. ${\mathrm{Li}}_2\mathrm{O},{\mathrm{Na}}_2\mathrm{O}\mathrm{and}{\mathrm{K}}_2{\mathrm{O}}_2$
• D. ${\mathrm{Li}}_2\mathrm{O},{\mathrm{Na}}_2{\mathrm{O}}_2\mathrm{and}{\mathrm{K}}_2\mathrm{O}$

Answer 1

The correct option is B

${\mathrm{Li}}_2\mathrm{O},{\mathrm{Na}}_2{\mathrm{O}}_2\mathrm{and}{\mathrm{KO}}_2$

Explanation for correct answer:-

Option (B) ${\mathrm{Li}}_2\mathrm{O},{\mathrm{Na}}_2{\mathrm{O}}_2\mathrm{and}{\mathrm{KO}}_2$

• Lithium upon combustion in excess air produces Lithium oxide$\left({\mathrm{Li}}_2\mathrm{O}\right)$
• The complete reaction is:

$\underset{\mathrm{Lithium}}{2\mathrm{Li}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{\frac{1}{2}{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Lithium}\mathrm{oxide}}{{\mathrm{Li}}_2\mathrm{O}\left(\mathrm{s}\right)}$

• Sodium upon combustion in excess air produces Sodium peroxide$\left({\mathrm{Na}}_2{\mathrm{O}}_2\right)$
• The complete reaction is:

$\underset{\mathrm{Sodium}}{2\mathrm{Na}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Sodium}\mathrm{peroxide}}{{\mathrm{Na}}_2{\mathrm{O}}_2\left(\mathrm{s}\right)}$

• Potassium upon combustion in excess air produces Potassium superoxide$\left({\mathrm{KO}}_2\right)$
• The complete reaction is:

$\underset{\mathrm{Potassium}}{\mathrm{K}\left(\mathrm{s}\right)}+\underset{\mathrm{Oxygen}}{{\mathrm{O}}_2\left(\mathrm{g}\right)}\to \underset{\mathrm{Potassium}\mathrm{superoxide}}{{\mathrm{KO}}_2\left(\mathrm{s}\right)}$

• Hence it is the correct option

Therefore, On combustion of Li, Na and K in excess of air, the major oxides formed, respectively, are option (B) ${\mathrm{Li}}_2\mathrm{O},{\mathrm{Na}}_2{\mathrm{O}}_2\mathrm{and}{\mathrm{KO}}_2$