Question

Iron is rendered passive by the treatment with:

• A. conc. $HCl$
• B. conc. $HN{O}_3$
• C. conc. $H_{2}S{O}_4$
• D. conc. $H_{3}P{O}_4$

Answer 1

The correct option is B conc. $HN{O}_3$

Iron is the metal which is rendered passive with concentrated nitric acid. Iron readily dissolves in dilute nitric acid and the concentrated acid forms a metal oxide layer that protects the bulk of the metal from further oxidation. The formation of this protective layer is called as passivation.