The instrument to draw a circle is
Ruler
Protractor
Divider
Compasses
A circle is the set of all points that are at the same distance from a fixed point (the centre).
To draw a circle, we need an instrument that can:
Fix one leg at the centre (O).
Keep the pencil at a fixed distance (the radius) (r).
Rotate around (O) to mark all points at distance (r).
Check each option:
Ruler: used to draw/measure straight lines, not circles.
Protractor: used to measure angles in degrees, not to draw circles.
Divider: used to transfer or compare distances, not to draw a circle.
Compasses: a hinged two-leg tool with a needle and a pencil — exactly what we need to draw a circle.
How compasses work (small steps):
Set the centre: (O)
Choose the radius: (r)
Keep the needle at (O)
Keep the pencil (r) units away
Rotate a full turn: (360^circ)
All points are at distance (r) from (O) ⇒ a circle is formed.