We can define the standard deviation as the square root of the variance.
The unit for standard deviation and mean are same. But the variance is expressed in square units.
The variance cannot be negative, because then, you cannot find the square root of it.
Similarly, under no circumstances, the standard deviation can be negative. The standard deviation formula is calculated by using squares of the numbers, and square of a number cannot be negative.
<span>Standard deviation is the square root of variance. Variance is always a non-negative number, since you can't take the square root of a negative number. So neither can be negative </span>
