In the birth weight of each of the 10 babies born in a hospital in a day is found to be 2.8 kgs, then the standard deviation of this sample will be -
Standard deviation measures the variation (dispersion) of an individual data from the mean.
SD tells how tightly all the values are clustered around the mean in a set of data.
High standard deviation indicates that the data is dispersed away from the mean.
Low standard deviation indicates that the data points tend to be very close to mean, i.e. data points are clustered close to the mean.
For example, the average height for adult men in USA is about 70 inches, and standard deviation is 3 inches. Then -


If dispersion of mean is 1 SD → most men (about 68%) have a height within 3 inches of the mean (67-73) inches.
If dispersion of mean is 2 SD → almost all men (95%) have a height within 6 inches of the mean (64 - 76) inches.
If dispersion is zero SD all men would be exactly 70 inches.


That means greater the standard deviation greater will be the data spread away from standard deviation.

Coming back to question

Here all newborn babies has 2.8 kgs of weight.
That means there is no dispersion from mean.
So, standard deviation is zero.
2.8
0
1
0.28