Relational Algebra

The correct option is (D) :6.

- Statement A is true, as the selection operation yields horizontal subsets.
- Statement B is false, as selection operates horizontally.
- Statement C is false, union can only work with relations of the same degree.
- Statement D is false, intersection and Cartesian product are binary operations.
- Statement E is false; a record is a row, not a column.

To find the result of the set difference operation HISTORY - SCIENCE, follow these steps:
1. The set difference operation will return rows from the HISTORY table that are not present in the SCIENCE table.
2. Compare each row from HISTORY with every row in SCIENCE.
3. Identify rows in HISTORY with no matching row in SCIENCE based on 'NAME' and 'CLASS'.

The rows in HISTORY are:
- (1, MOHAN, 6A)
- (2, SANJAY, 6B)
- (3, YOGESH, 7A)

The rows in SCIENCE are:
- (1, NARESH, 6B)
- (2, SANJAY, 6B)
- (3, YOGESH, 7A)

By comparing,
- (1, MOHAN, 6A) is present in HISTORY but not in SCIENCE.
- (2, SANJAY, 6B) is present in both tables.
- (3, YOGESH, 7A) is present in both tables.

Thus, the only row not present in SCIENCE is:

SNo	NAME	CLASS
1	MOHAN	6A