Birth weight of all 10 babies born in a nursing home on a day was 2.7 kg. Standard deviation is –

**Core Concept**
In statistics, the standard deviation (SD) is a measure of the amount of variation or dispersion of a set of values. A low standard deviation indicates that the values tend to be close to the mean, while a high standard deviation indicates that the values are spread out over a wider range.

**Why the Correct Answer is Right**
Since all 10 babies have the same birth weight of 2.7 kg, there is no variation in the data. In such a case, the standard deviation is zero, as there is no deviation from the mean. The formula for standard deviation is the square root of the sum of the squared differences from the mean divided by the number of observations. Since all observations are the same, the squared differences from the mean are zero, and the standard deviation is also zero.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it would imply that there is some variation in the birth weights, which is not the case.
* **Option B:** This option is incorrect because it would imply that the standard deviation is greater than zero, which is not possible if all observations are the same.
* **Option C:** This option is incorrect because it is a positive value, which is not possible for the standard deviation of a set of identical values.
* **Option D:** This option is incorrect because it is a negative value, which is not possible for the standard deviation.

**Clinical Pearl / High-Yield Fact**
When dealing with a set of identical values, it is essential to remember that the standard deviation is zero, as there is no variation in the data.

**Correct Answer: A. 0**