what are the merits and demerits of correlation?

Dear Student,

I think you might be asking about the merits and demerits of each method of measuring correlation.

For merits and demerits of scatter diagram of measuring correlation, follow the link.
https://www.meritnation.com/cbse/class11-commerce/studymaterial/economics/statistics-for-economics/correlation/443_2499_6439#slide1_Methods of Measuring Correlation Scattered Diagram and Karl Pearson's Coefficient of Correlation

For merits and demerits of Karl Pearson's Correlation Coefficient of measuring correlation, follow the link.
https://www.meritnation.com/cbse/class11-commerce/studymaterial/economics/statistics-for-economics/correlation/443_2499_6439#slide1_Methods of Measuring Correlation Scattered Diagram and Karl Pearson's Coefficient of Correlation

For merits and demerits of Spearman's Rank Correlation Coefficient of measuring correlation, follow the link.
https://www.meritnation.com/cbse/class11-commerce/studymaterial/economics/statistics-for-economics/correlation/443_2499_6440#slide1_Spearman's Rank Correlation Coefficient

All the best for your exams!!