The decrease in atomic volume from $Cr$ to $Cu$ in the $3d$ series is very negligible because:

Given below are two statements: one is labelled as Assertion $A$ and the other is labelled as Reason $R$.
Assertion $A$: In $T \ell I_{3}$,isomorphous to $CsI_{3}$,the metal is present in $+1$ oxidation state.
Reason $R$: $T \ell$ metal has fourteen $f$ electrons in the electronic configuration.
In the light of the above statements,choose the most appropriate answer from the options given below:

Which of the following is the common oxidation state for transition elements?

Which of the following elements has the maximum first ionisation potential?

Which of the following does not represent the correct order of the property indicated?

In which pair of ions are both diamagnetic in nature?