Name a transition element which does not exhibit variable oxidation states.

State the reason for the stability of the $Gd^{3+}$ ion.

Which element exhibits a $+7$ oxidation state?

The chloride of which of the following elements will be coloured?

Predict which of the following will be coloured in aqueous solution: $Ti^{3+}, V^{3+}, Cu^{+}, Sc^{3+}, Mn^{2+}, Fe^{3+},$ and $Co^{2+}$. Give reasons for each.

Identify the correct order of atomic radii for the following $3d$ series elements.