The instruments used to bisect a given line segment.
A) Scale and protractor
B) Scale and compass
C) Scale and set-square
D) Scale

Hint: We will first get to know about every tool and its uses. After that we will think about drawing a circle from it. If we see that it is possible, we will just go ahead with that option.

Complete step-by-step answer:
We will evaluate each option one by one and then see if we can use it.
A) Scale and protractor
A protractor is a measuring instrument, typically made of transparent plastic or metal, for measuring angles. Here is a picture for your reference:-

We cannot bisect a line segment with it as well as it is made for measuring angles.
So, the scale and protractor is discarded.
B) Scale and compasses
Draw a line segment using a scale.
Take the compass length more than half of the line segment.
Place the compass at one endpoint and draw an arc above and below the line.
Without making any changes in the compass, place the compass at the other end and draw an arc above and below the line.
Now, draw a line using a scale to join the points where the arc had intersected.
So, the joined line is the bisector of the line segment.
So, the required tools are scale and compass.
C) Scale and set-square

Setsquare: A set square or triangle (American English) is an object used in engineering and technical drawing, with the aim of providing a straightedge at a right angle or other particular planar angle to a baseline. Here is a picture for your reference:-

We cannot bisect a line segment with it as well as it is providing straight edges.
So, the scale and Set square is discarded.
D) Scale
A scale can be used to draw the line segment.
We cannot bisect a line segment with it .

Option B is the correct answer.

Note: The students might make mistakes in compass after drawing from one endpoint, it will not bisect the line. Also, by scale only, it is quite difficult to mark the exact midpoint of the line segment. So, it is better to not use the scale only to bisect the line segment.