Which one of the following ions exhibits $d-d$ transition and paramagnetism as well?

What is the use of potassium dichromate $(K_2Cr_2O_7)$?

When a small amount of vanadium is added to steel,it becomes:

Which one of the following is known as lunar caustic when in fused state?

The colorless species is

Determine the correct $(T)$ and incorrect $(F)$ statements from the following:
$(a)$ The $E^o$ for $MnO_4^- + 8H^+ + 5e^- \to Mn^{2+} + 4H_2O$ is $-1.52 \ V$.
$(b)$ $MnO_4^-$ oxidizes $I^-$ to $I_2$.
$(c)$ The color of $CrO_4^{2-}$ is yellow in the presence of $H^+$.
$(d)$ The color of $CrO_4^{2-}$ is yellow in the presence of $OH^-$.