The correct answer is A.
The probable error of the coefficient of correlation is a measure of how much the correlation coefficient is likely to vary from sample to sample. It is calculated by the following formula:
$$\text{PE}(r) = 0.6745\sqrt {\frac{{1 – {r^2}}}{n}}$$
where $r$ is the correlation coefficient and $n$ is the number of pairs of data points.
Option B is incorrect because it does not divide by $\sqrt{n}$. Option C is incorrect because it adds $r^2$ instead of subtracting it. Option D is incorrect because it divides by $n$ instead of $\sqrt{n}$.
The probable error of the coefficient of correlation is used to interpret the significance of the correlation coefficient. A correlation coefficient that is greater than the probable error is considered to be statistically significant.