Which fo the following metal is rendered passive by the action of highly concentrated nitric acid (~80%)?

Options

A. `Fe`
B. `Al`
C. `Ni`
D. All of these

Answer

4

Explanation

Nitric acid of any concentration has no effect on very unreactive metals such as gold and platinum. The concentrated acid has no effect either on aluminimum ,iron or nickel ,this is unexpected .it is thought that the surface of these three metals is first attacked,a thin impervious oxide film being formed which stops further action, the phenomenon is referred to as passivity.
Other metals which become passive are cobalt and chromium