Manganese achieves its highest oxidation state in which of the following compounds?

Which from the following alloys is used in gas turbine engines?

Which lanthanoid compound is used in pigments?

Excess of $KI$ reacts with $CuSO_4$ solution and then $Na_2S_2O_3$ solution is added to it. Which of the statements is incorrect for this reaction?

Fill in the blanks:
$1.$ The copper layer on copper coins in the $UK$ is .......... .
$2.$ Copper-silver coins in the $UK$ are an alloy of ............ .
$3.$ The catalyst used for the oxidation of $SO_2$ to $SO_3$ is ......... .

Determine the correct $(T)$ and incorrect $(F)$ statements from the following:
$(a)$ In the titration of $C_2O_4^{2-}$ with $KMnO_4$,$C_2O_4^{2-}$ acts as an oxidizing agent.
$(b)$ $KMnO_4$ is a strong oxidizing agent.
$(c)$ In $Cr_2O_4^{2-}$,the $O-Cr-O$ bond angle is $120^o$.
$(d)$ The standard electrode potential for the reaction $Cr_2O_7^{2-} + 14H^+ + 6e^- \to 2Cr^{3+} + 7H_2O$ is $E^o = -1.33 \ V$.