The correct answer is option 1.
Concept:
Natural Join (* or ⋈):
Natural Join (⋈) We can perform a Natural Join only if there is at least one common attribute that exists between two relations. In addition, the attributes must have the same name and domain. Natural join acts on those matching attributes where the values of attributes in both the relations are the same.
The given relations schemas are,
R(A, B, C, D) and S(D, E, F) Here common attribute is D, upon matching attributes where the values of attributes in both the relations are the same. After matching the two relations the new relation becomes, RS (A, B, C, D, E, F).
Degree of schema:
The degree is the total number of attributes/fields of a relation/table and cardinality is the total number of tuples/rows of relation/table.
The resultant schema R*S =RS (A, B, C, D, E, F)
So the number of attributes = 6.
Hence the correct answer is 6.