Which of the following combinations is common for jewelry alloys?

The correct choice highlights a common combination used in jewelry alloys, particularly gold mixed with silver, copper, and zinc. These metals are commonly alloyed with gold to enhance its color, strength, and workability.

Gold is a relatively soft metal on its own, so alloying it with other metals allows jewelers to create pieces that are not only aesthetically pleasing but also more durable. Silver provides a lustrous finish and can enhance the overall appearance of the jewelry. Copper is often added to give a warmer tone and also increases the hardness of the alloy, making it more suitable for everyday wear. Zinc can be included to improve casting properties and prevent oxidation, contributing to the alloy's longevity and maintenance.

In contrast, combinations that include metals such as aluminum, potassium, iron, manganese, lead, or mercury are not typically used in jewelry due to their undesirable properties, such as high reactivity, low aesthetic appeal, or toxicity. Thus, the choice of gold combined with silver, copper, and zinc is a well-established practice in the jewelry making industry, making it the optimal answer.