The correct answer is $\boxed{\text{B) 0.64}}$.
The coefficient of correlation is a measure of the strength of the linear relationship between two variables. It is a number between -1 and 1, inclusive. A coefficient of correlation of 0 indicates that there is no linear relationship between the variables. A coefficient of correlation of 1 indicates that there is a perfect positive linear relationship between the variables. A coefficient of correlation of -1 indicates that there is a perfect negative linear relationship between the variables.
In this case, the unexplained variation between variables X and Y is 36%. This means that 36% of the variation in variable Y cannot be explained by the variation in variable X. This suggests that there is a weak linear relationship between the variables. The coefficient of correlation between the variables is therefore likely to be close to 0.
Option A is incorrect because it is the coefficient of correlation for a perfect positive linear relationship. Option C is incorrect because it is the coefficient of correlation for a weak positive linear relationship. Option D is incorrect because it is the coefficient of correlation for a perfect negative linear relationship.