The electronic configuration of $Pt$ (atomic number $78$) is $...$

Which of the following elements does not exhibit variable valency?

Super alloys are usually

Illustrate by taking examples of transition elements and non-transition elements that oxidation states of elements are largely based on electronic configuration.

Which element from the following forms colourless compounds in $+2$ oxidation state?

If the colours of salts of transition elements are due to the presence of unpaired electrons in the transition metal ions,which of the following ions will be colourless in aqueous solution? (The atomic numbers of $Ti$ and $Fe$ are $22$ and $26$ respectively.)