Circles have infinitely many arcs, not just 3.
Adjacent Arcs
No
Diameter
Trefoil
Major arc is the longer of two arcs.
Yes, there can be congruent arcs on a circle. Arcs which subtend the same angle at the center are considered as congruent.
Circles have infinitely many arcs, not just 3.
Congruent Arcs
Adjacent Arcs
Half of the circle is an arc
No
Divide the arc's degree measure by 360°, then multiply by the circumference of the circle.
Diameter
Because they are parts of the circumference of a circle
In the same circle, or in congruent circles, two minor arcs are congruent if and only if their corresponding chords are congruent.
Trefoil