Final answer:
About 1/4 teaspoon of Cream of Tartar is used for whipping 2 egg whites, as it helps stabilize and maintain their structure. This is the closest amount to the typical recommendation of 1/8 to 1/4 teaspoon per egg white.
Step-by-step explanation:
The amount of Cream of Tartar required when whipping 2 egg whites is typically about 1/8 to 1/4 teaspoon. Since none of the options provided match this recommendation and assuming the options cannot be modified, we would go with the closest amount which is 1/4 teaspoon (option a).
When whipping egg whites, Cream of Tartar is used to stabilize the egg whites and help them hold their peak structure. The appropriate quantity of Cream of Tartar can vary slightly based on the recipe or desired firmness of the egg whites, but a general guideline is 1/8 to 1/4 teaspoon per egg white.