Answer: The argument is valid by the law of detachment
Explanation:
The law of detachment simply states that when the hypothesis is true, then the conclusion must also be true.
In this case, the argument is valid since the conclusion that "Quadrilateral JKLM is a square" follows from the argument that "a quadrilateral is a square, then the quadrilateral has four right angles".
The law of detachment is expressed here.