Which of the following is a neutral oxide?

The correct option is D

$\mathrm{CO}$

The explanation for correct answer:

(d) $\mathrm{CO}$

1. Neutral oxides are formed when some compounds react with Oxygen to generate oxides that are neither acidic nor basic. In other words, neutral oxides are those that do not form acids or bases when it reacts with water.
2. Carbon monoxide ($\mathrm{CO}$ ) when reacts with water it gives Carbon dioxide and Hydrogen, so it is a neutral oxide.

$$\begin{gathered} \mathrm{CO}\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\rightleftharpoons {\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{Carbon}\mathrm{Carbon} \\ \mathrm{monoxide}\mathrm{dioxide} \end{gathered}$$

The explanation for incorrect answer:

(a) $\mathrm{SrO}$

1. It is a basic oxide.
2. It produces base when it reacts with water.

$$\begin{gathered} \mathrm{SrO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Sr}{\left(\mathrm{OH}\right)}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\left(\mathrm{g}\right) \\ \mathrm{Strontium}\mathrm{Strontium} \\ \mathrm{oxide}\mathrm{hydroxide} \end{gathered}$$

(b) ${\mathrm{Al}}_2{\mathrm{O}}_3$

1. It is an amphoteric oxide.
2. It shows the properties of both acidic and basic oxides
3. Reaction with acid :
   $$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+3{\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)\to {\mathrm{Al}}_2{\left({\mathrm{SO}}_4\right)}_3\left(\mathrm{aq}\right)+3{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Aluminium}\mathrm{Aluminium} \\ \mathrm{oxide}\mathrm{sulphate} \end{gathered}$$
4. Reaction with base:

$$\begin{gathered} {\mathrm{Al}}_2{\mathrm{O}}_3\left(\mathrm{s}\right)+2\mathrm{NaOH}\left(\mathrm{aq}\right)\to 2{\mathrm{NaAlO}}_2\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Aluminium}\mathrm{Sodium}\mathrm{aluminium} \\ \mathrm{oxide}\mathrm{oxide} \end{gathered}$$

(c) ${\mathrm{CO}}_2$

1. It is an acidic oxide.
2. It produces acid when it combines with water.

$$\begin{gathered} {\mathrm{CO}}_2\left(\mathrm{g}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to {\mathrm{H}}_2{\mathrm{CO}}_3\left(\mathrm{aq}\right) \\ \mathrm{Carbon}\mathrm{Cabonic} \\ \mathrm{dioxide}\mathrm{acid} \end{gathered}$$

Therefore, Option (d) is correct. CO is a neutral oxide.