Introduction:
Measures of central tendency are statistical measures that help us understand the central or typical value of a dataset. They provide a summary of the data by giving us an idea of where most of the data points lie. The main measures of central tendency are the mean, median, and mode.

Explanation:
The correct answer is option 'D', which states that the standard deviation is not a measure of central tendency. Let's understand why this is the case:

Mean:
The mean is the sum of all the data values divided by the total number of values. It represents the arithmetic average of the dataset. The mean is a measure of central tendency as it shows the center or typical value around which the data points tend to cluster.

Median:
The median is the middle value in a dataset when the data points are arranged in ascending or descending order. It divides the dataset into two equal halves. The median is another measure of central tendency as it represents the value that lies at the center of the dataset.

Mode:
The mode is the value that occurs most frequently in a dataset. It represents the peak or most common value in the dataset. The mode is also a measure of central tendency as it shows the value around which the data points cluster the most.

Standard Deviation:
The standard deviation, on the other hand, is a measure of dispersion or variability in a dataset. It quantifies the average amount by which each data point deviates from the mean. It provides information about the spread of the data points around the mean, rather than focusing on a particular central value. Thus, the standard deviation is not a measure of central tendency.

Conclusion:
In summary, the standard deviation is not a measure of central tendency. It is a measure of dispersion or variability in a dataset. The mean, median, and mode are the main measures of central tendency, representing the center or typical value of a dataset.