An iron nail is kept in each of the following liquids. In which case would it lose its shine and appear dull?

The correct option is B

Soft drink

Explanation for correct option

(B)Soft drink

Carbonic acid

• Carbonic acid is a weak acid, an aqueous solution of carbon dioxide.
• Carbonic acid is a better electrolyte than water. The acid breaks water into hydrogen and oxygen. Free oxygen reacts with iron and releases free electrons.
• These free electrons initiate corrosion of the metal.
• An iron nail kept in a soft drink loses its shine and appears dull. Because Soft drink has carbonic acid.
• This acid reacts with iron to form iron carbonate. Hence nail appears dull.

Explanation for incorrect options

• Mustard oil does not react with iron.
• Kerosene breaks contact between iron and oxygen hence preventing the formation of rust.
• Coconut oil does not react with iron.
• Hence, options (A), (C), and (D) are incorrect.

Hence option (B) is correct. Iron nail loses its shine and appears dull in soft drinks.