Which of the following compounds is coloured?

Which of the following pairs of ions are colourless?

How is the variability in oxidation states of transition metals different from that of the non-transition metals? Illustrate with examples.

The correct statement about iron includes:
$I$) The highest oxidation state of iron is $+ 6$ in $K_2FeO_4$.
$II$) The iron shows $+ 2$ oxidation state with six electrons in the $3d$ orbitals.
$III$) The common oxidation state of iron is $+ 3$ with five unpaired electrons in the $3d$ orbital.

In the $3d$ series of transition elements,the atomic radii from $Cr$ to $Cu$ are approximately the same because:

In the $3d$ transition series,as the atomic number increases,the paramagnetic character: