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

$A$ group of acidic oxides is

Consider the following chemical reactions involved in the extraction of chromium from chromite ore:
$(a)$ $4FeCr_2O_4 + X_1 + 7O_2 \to 8Na_2CrO_4 + 2Fe_2O_3 + 8CO_2$
$(b)$ $2Na_2CrO_4 + X_2 \to Na_2Cr_2O_7 + 2Na^+ + H_2O$
Identify the species $X_1$ and $X_2$ in the reactions.

Copper sulphate is not used:

Assertion: $KMnO_4$ is purple in colour due to charge transfer.
Reason: There is no electron present in $d$-orbitals of Manganese in $MnO_4^-$.

Corundum is