Nickel is refined by

The correct answer is Option (4) → Mond Process for Refining

In the Mond process, impure nickel is heated in a stream of carbon monoxide; it forms the volatile complex nickel tetracarbonyl. The vapour is then heated to a higher temperature, where the complex decomposes and gives pure nickel:

    \( \ce{Ni + 4CO} \xrightarrow{330-350\ \mathrm{K}} \ce{Ni(CO)4} \)

    \( \ce{Ni(CO)4} \xrightarrow{450-470\ \mathrm{K}} \ce{Ni + 4CO} \)

Note: This question is from the pre-rationalised NCERT book (2022-23). The topic is not there in the latest NCERT book (2026-27), and it is also out of the CUET 2026 syllabus.

NCERT (Pre-rationalised edition, 2022-23):
Mond Process for Refining Nickel