Find the value of spin-only magnetic moment for chromium cation in $+2$ state. (in $BM$)

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 one of the following ions is colourless?

The $3d-$ elements show variable oxidation states. What is the maximum oxidation state shown by the element $Mn$?

Which of the following statements concern with transition metals?

In the following pairs,the one in which both transition metal ions are colourless is