Solution

The correct answer is EC

Key Points 

EXPLANATION:

In order to find the key for a relational schema, we need to find a minimal set of attributes which can determine all other attributes. This is usually done by calculating the closure of each set of attributes.Given the functional dependencies:

• C → F, E → A, EC → D, A → B

Let's compute the closure of each candidate key:

• For CD closure: CD C gives F by the dependency C → F. But no other attributes can be determined. So, CD closure is CDF. It does not include all attributes.
• For EC closure: EC E gives A by the dependency E → A, and EC gives D by the dependency EC → D. Then, A gives B. Now we have ECABDF which includes all the attributes. 

So, the key for R is EC.

Mistake PointsAbove Official question some mistake in data R (A, B, C, D, F)  the relation mention attribute F but option they don't give F in any key pair so we have change the relation R (A, B, C, D, E, F) and solve them.