A. The measure of dispersion can never be negative. It is never negative since every term in the variance sum is squared and therefore either positive or zero. It has squared units.
A. Discrete and continuous are the two types of a random variables. A percentile is definitely a quantile. R can approximate quantiles for common distribution
Correlation can tell you something about the relationship between variables. It is used to understand:
1. Whether the relationship is positive or negative
2. The strength of the relationship.