How many of the following can react with bases?

$\left(1\right){\mathrm{Al}}_2{\mathrm{O}}_3\left(2\right)\mathrm{MgO}\left(3\right)\mathrm{BeO}\left(4\right){\mathrm{SeO}}_2\left(5\right){\mathrm{NO}}_2\left(6\right)\mathrm{PbO}\left(7\right){\mathrm{As}}_2{\mathrm{O}}_3$

Reactivity with bases:

• Bases react with either acids or amphoteric oxides.
• Amphoteric oxides react with both acids and bases, in reaction with acids they act as a base while bases act as acids.
• ${\mathrm{Al}}_2{\mathrm{O}}_3$ : It reacts with base Sodium hydroxide to give Sodium aluminium hydroxide.

${\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{NaAl}{\left(\mathrm{OH}\right)}_4\left(\mathrm{s}\right)$

• $\mathrm{MgO}$: It does not reacts with any basic compound because Magnesium oxide itself is the base.
• $\mathrm{BeO}$ : It reacts with a base like Sodium hydroxide, due to its acidic nature.

$\mathrm{BeO}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{BeO}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

• ${\mathrm{SeO}}_2$: Base does not react with Selenium oxide.
• ${\mathrm{NO}}_2$: Nitrogen oxide reacts with Sodium hydroxide to give Sodium nitrate, Sodium nitrite, and water.

${\mathrm{NO}}_2\left(\mathrm{g}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{NaNO}}_2\left(\mathrm{s}\right)+{\mathrm{NaNO}}_3\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

• $\mathrm{PbO}$: When Lead oxide reacts with Sodium hydroxide there is the formation of salt and water.

$\mathrm{PbO}\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to {\mathrm{Na}}_2{\mathrm{PbO}}_2\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

• ${\mathrm{As}}_2{\mathrm{O}}_3$: Arsenic oxide is amphoteric in nature, it reacts with Sodium hydroxide to give Arsenite.

${\mathrm{As}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+6\mathrm{NaOH}\left(\mathrm{aq}\right)\to 2{\mathrm{Na}}_3{\mathrm{AsO}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)$

• Therefore, only ${\mathrm{Al}}_2{\mathrm{O}}_3,\mathrm{BeO},{\mathrm{NO}}_2,\mathrm{PbO},{\mathrm{As}}_2{\mathrm{O}}_3$ reacts with a base.

Hence, only five of the above compounds react with the base.