$\mathrm{Fe}^{3+}$

$\mathrm{Mn}^{3+}$

$\mathrm{Ni}^{2+}$

$\mathrm{Co}^{3+}$

A is true but R is false

Both $A$ and $R$ are true, $R$ is the correct explanation of $A$

Both $A$ and $R$ are true but $R$ is not the correct explanation of $A$

A is false but R is true

$\mathrm{Cr}(\mathrm{OH})_2$

$\mathrm{Cr}(\mathrm{OH})_3$

$\mathrm{CrO}_4{ }^{2-}$

$\mathrm{CrO}_3$

$\mathrm{VO}>\mathrm{CrO}>\mathrm{TiO}>\mathrm{FeO}$

$\mathrm{FeO}>\mathrm{CrO}>\mathrm{VO}>\mathrm{TiO}$

$\mathrm{TiO}>\mathrm{VO}>\mathrm{CrO}>\mathrm{FeO}$

$\mathrm{CrO}>\mathrm{TiO}>\mathrm{FeO}>\mathrm{VO}$