What is the highest oxidation state exhibited by any transition element among all?

The correct statement$(s)$ about $Cr^{2+}$ and $Mn^{3+}$ is(are)
[Atomic numbers of $Cr = 24$ and $Mn = 25$]
$(A)$ $Cr^{2+}$ is a reducing agent
$(B)$ $Mn^{3+}$ is an oxidizing agent
$(C)$ Both $Cr^{2+}$ and $Mn^{3+}$ exhibit $d^4$ electronic configuration
$(D)$ When $Cr^{2+}$ is used as a reducing agent,the chromium ion attains $d^3$ electronic configuration

Most transition metals exhibit several characteristic properties. Which of the following statements are correct?
$I$: Form sets of compounds which display different oxidation states of the metal.
$II$: Form coloured ions in solution.
$III$: Burn vigorously in oxygen.
$IV$: Act as catalysts.

The higher oxidation states of transition elements are found to be in combination with $A$ and $B,$ which are

Which of the following metals forms more than one chloride?

The number of electrons in the outermost shell of the $3d-$ transition elements generally remains: