Which forms interstitial compounds?

Platinum, Palladium and Iridium are called noble metals because

Identify the correct statements from the following: $(i)$ $Ti(IV)$ is more stable than $Ti(III)$ and $Ti(II)$ $(ii)$ Among $3d-$series elements (from $Z=22$ to $29$) only copper has positive reduction potential $(M^{2+} / M)$ $(iii)$ Both $Sc$ and $Zn$ exhibit $+1$ oxidation state

Which of the following general configurations of the outermost shell represents the chromium element [$Cr$'s atomic number $= 24$]?

Which of the following elements does not belong to the first transition series?

Which elements of the $3d$ series do not show variable valency?