Iron is rendered passive by treatment with

Identify the basic oxide from the following:

Identify the correct statement.

Assertion $(A)$: $CuI_2$ cannot be prepared by the reaction of $Cu^{2+}_{(aq)}$ with $I^{-}_{(aq)}$.
Reason $(R)$: Aqueous $Cu^{2+}$ solution is blue in colour.
The correct answer is:

Explain the catalytic properties of transition metals.

Iron is rendered passive by the action of