Which property indicates that the grouping of addends does not affect their sum?

The property that indicates that the grouping of addends does not affect their sum is known as the Associative Addition property. This property allows us to regroup the numbers being added without changing the total. For instance, if you have three numbers, say a, b, and c, the Associative property states that (a + b) + c is the same as a + (b + c). Regardless of how you group the addends, the sum remains constant.

This understanding is critical in simplifying expressions and solving equations, as it allows for flexibility in calculation. The other properties, while important in their own right, pertain to different aspects of arithmetic. The Commutative Property deals with the order of the numbers being added or multiplied, the Distributive Property relates to how multiplication distributes over addition, and the Zero Property refers to the behavior of zero in addition and multiplication. Therefore, the Associative property uniquely focuses on the grouping of numbers in addition, confirming the correct choice.