Question

Iron is not protected from rusting by:

• A. galvanization
• B. electroplating with $Ni$ or $Cr$
• C. heating the iron to redness in steam
• D. treating it with $H_{3}P{O}_4$

Answer 1

The correct option is D treating it with $H_{3}P{O}_4$

Phosphoric acid will not form a protective coating of iron oxide on the surface of iron. A strong oxidizing agent such as nitric acid is required for this process.