Which of the following are basic oxides?

${\mathrm{Mn}}_2{\mathrm{O}}_7,{\mathrm{V}}_2{\mathrm{O}}_3,{\mathrm{V}}_2{\mathrm{O}}_5,{\mathrm{Cr}}_2{\mathrm{O}}_3,\mathrm{CrO}$

Basic oxides of metal

• On moving along a period, the metallic character decreases.
• The basic character of metal oxide decreases along the period.
• The oxides of transition metals that contain metals in lower oxidation states are considered to be basic in nature.

${\mathbf{Mn}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{7}}$

• In ${\mathrm{Mn}}_2{\mathrm{O}}_7$, the oxidation state of manganese $\left(\mathrm{Mn}\right)$ is as follows:

$\begin{array}{rcl}2\left(\mathrm{x}\right)+7(-2)& =& 0\\ 2\mathrm{x}-14& =& 0\\ \mathrm{x}& =& \frac{14}{2}\\ & =& 7\end{array}$

• The oxidation state of $\mathrm{Mn}$ in ${\mathrm{Mn}}_2{\mathrm{O}}_7$ is $+7$.
• The manganese is present in its highest oxidation state.
• The manganese tends to accept the pair of electrons.
• Hence it is an acidic oxide.

${\mathbf{V}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}$

• In ${\mathrm{V}}_2{\mathrm{O}}_3$, the oxidation state of Vanadium $\left(\mathrm{V}\right)$ is as follows:

$\begin{array}{rcl}2\left(\mathrm{x}\right)+3(-2)& =& 0\\ 2\mathrm{x}-6& =& 0\\ \mathrm{x}& =& \frac{6}{2}\\ & =& 3\end{array}$

• The oxidation state of $\mathrm{V}$ in ${\mathrm{V}}_2{\mathrm{O}}_3$ is $+3$.
• The Vanadium is present in its lowest oxidation state.
• The Vanadium tends to donate the pair of electrons.
• Hence it is basic oxide.

${\mathbf{V}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{5}}$

• In ${\mathrm{V}}_2{\mathrm{O}}_5$, the oxidation state of Vanadium $\left(\mathrm{V}\right)$ is as follows:

$\begin{array}{rcl}2\left(\mathrm{x}\right)+5(-2)& =& 0\\ 2\mathrm{x}-10& =& 0\\ \mathrm{x}& =& \frac{10}{2}\\ & =& 5\end{array}$

• The oxidation state of $\mathrm{V}$ in ${\mathrm{V}}_2{\mathrm{O}}_5$ is $+5$.
• The Vanadium tends to donate and accept the pair of electrons.
• Hence it is amphoteric oxides.

${\mathbf{Cr}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}$

• In ${\mathrm{Cr}}_2{\mathrm{O}}_3$, the oxidation state of Chromium $\left(\mathrm{Cr}\right)$ is as follows:

$\begin{array}{rcl}2\left(\mathrm{x}\right)+3(-2)& =& 0\\ 2\mathrm{x}-6& =& 0\\ \mathrm{x}& =& \frac{6}{2}\\ & =& 3\end{array}$

• The oxidation state of $\mathrm{Cr}$ in ${\mathrm{Cr}}_2{\mathrm{O}}_3$ is $+3$.
• The Chromium tends to donate and accept the pair of electrons.
• Hence it is amphoteric oxides.

$\mathbf{CrO}$

• In $\mathrm{CrO}$, the oxidation state of Chromium $\left(\mathrm{Cr}\right)$ is as follows:

$\begin{array}{rcl}\mathrm{x}-2& =& 0\\ \mathrm{x}& =& 2\end{array}$

• The oxidation state of $\mathrm{Cr}$ in $\mathrm{CrO}$ is $+2$.
• The Chromium is present in its lowest oxidation state.
• The Chromium tends to donate the pair of electrons.
• Hence it is basic oxide.

Therefore, among the given oxides, $\mathbf{CrO}$ and ${\mathbf{V}}_{\mathbf{2}}{\mathbf{O}}_{\mathbf{3}}$ are basic oxides.