The standard deviation of a set of data is

The standard deviation of a set of data is a measure of dispersion. It tells us how much the data deviates from the mean. A high standard deviation indicates that the data is widely spread out, while a low standard deviation indicates that the data is clustered around the mean. It is not always measured from the mode or median, but rather from the mean of the data. Therefore, and (a) are incorrect. While the standard deviation is a type of average, it is not the most representative one, as it only tells us about the variability of the data, and not about its central tendency. Therefore, is also incorrect.