If a rectangle has four congruent sides, it is a square.

A square has perpendicular diagonals.

Conclusion: A rectangle has diagonals that are always perpendicular.

Which of the following is correct

The conclusion is valid by the law of syllogism.

The conclusion is invalid because not all rectangles are squares.

The conclusion is valid by the law of detachment.

The conclusion is invalid because all rectangles are squares.

The correct statement is:

The conclusion is invalid because not all rectangles are squares.

The correct answer is "The conclusion is invalid because not all rectangles are squares."

The law of syllogism states that if two statements are true and their middle terms are the same, then the conclusion is valid. However, in this case, the conclusion is not valid because not all rectangles are squares. A rectangle can have opposite sides that are congruent, but if the adjacent sides are not congruent, then it is not a square. Therefore, the conclusion that all rectangles have diagonals that are always perpendicular is incorrect.

Invalid, all not squares