Answer is:
Try square
Explanation:
The try-square is a precision instrument which is used to check the squareness of a surface and the flatness of surfaces.
![Which one of the following instruments is used to check squareness and flatness of the job?](https://mcqfinder.in/uploads/images/question-papers/isro-technician-b-turner-2015-set-1/isro-technician-b-turner-2015-set-1-id-40-e.jpg)