When items of jewellery made of metals such as copper or nickel are placed in a solution having a salt of gold, a thin film of gold is deposited by

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Q: 73 (CDS-I/2011)
When items of jewellery made of metals such as copper or nickel are placed in a solution having a salt of gold, a thin film of gold is deposited by

question_subject: 

Science

question_exam: 

CDS-I

stats: 

0,9,13,4,7,9,2

keywords: 

{'jewellery': [0, 0, 0, 1], 'metals': [1, 2, 2, 7], 'copper': [1, 0, 1, 1], 'nickel': [1, 0, 0, 0], 'gold': [8, 1, 7, 14], 'thin film': [0, 0, 0, 1], 'electric current': [0, 1, 0, 6], 'salt': [1, 0, 1, 1], 'items': [3, 4, 8, 15]}

Option 1, cooling to below 0 degree C, is incorrect because changing the temperature alone will not cause a film of gold to be deposited on the jewellery. The process of gold deposition requires a different method.

Option 2, heating above 100 degree C, is also incorrect because heating the jewellery alone will not cause gold to be deposited. Again, a different process is needed.

Option 4, just keeping it for 10 minutes, is not sufficient to deposit gold on the jewellery. Time alone is not the determining factor for gold deposition.

The correct answer is option 3, passing an electric current. This process is known as electroplating. The jewellery is placed in a solution containing a salt of gold, which acts as the source of gold ions. When an electric current is passed through the solution, the gold ions are attracted to the metal surface of the jewellery, causing a thin film of gold to be deposited onto it. The electric current helps facilitate the transfer of gold ions from the solution to the jewellery, resulting in the deposition of gold.