Which of the following is the most appropriate for measuring the strength and…

Pearson's r is the standard statistical measure specifically designed for assessing linear relationships between two continuous variables measured on interval or ratio scales. In contrast, Spearman's rho is typically reserved for ordinal data, while Phi applies strictly to nominal variables in contingency tables. Since the question explicitly specifies interval/ratio variables, Pearson's correlation coefficient is definitively the most appropriate choice.