What is the most common oxidation state of the $3\mathrm{d}$ series elements?

In acidic medium, ${\mathrm{H}}_{\mathrm{2}}{\mathrm{O}}_{\mathrm{2}}$ changes ${\mathrm{Cr}}_{\mathrm{2}}{{\mathrm{O}}_{\mathrm{7}}}^{\mathrm{2-}}\text{ to} {\mathrm{CrO}}_{\mathrm{5}}$ which has two $(-\mathrm{O}-\mathrm{O}-)$ bonds. Oxidation state of $\mathrm{Cr} \text{in }{\mathrm{CrO}}_{\mathrm{5}}$ is ____.

Identify the oxidation states of titanium ($\mathrm{Z} = 22$) and copper ($\mathrm{Z} = 29$) in their colourless compounds.

The following ion in its aqueous solution is colourless : (Atomic number: $\mathrm{Sc}=21, \mathrm{Fe}=26, \mathrm{Ti}=22, \mathrm{Mn}=25$)

The colour of light absorbed by an aqueous solution of ${\mathrm{CuSO}}_{\mathrm{4}}$ is ______.

Identify the metal that forms colourless compounds (in its $+3$oxidation state).

Select the coloured compound amongst the following.

(Atomic no. $\mathrm{Ti}=22, \mathrm{Cr}=24, \mathrm{Cu}=29, \mathrm{Zn}=30$)

Which metal is used as a part of the catalyst in the Fischer-Tropsch method?

Which of the following ion is diamagnetic?