Final answer:
The breadth of a sampling distribution made up of an infinite number of mean differences between an infinite number of paired samples is the standard deviation.
Step-by-step explanation:
The breadth of a sampling distribution made up of an infinite number of mean differences between an infinite number of paired samples is the standard deviation.
The standard deviation measures how far the outcomes of a statistical experiment are from the mean of the distribution. In the context of a sampling distribution, it represents the average standard deviation that arises from repeated sampling.
Therefore, option (a) Standard Deviation is the correct answer.