The correct option is B Both A and R are true, and R is not the correct explanation for A.
The correct option is B.
Consider assertion (A) statement.
The external angle of a triangle = sum of opposite interior angles. It is given that two interior opposite angles of a triangle are equal.
Let x be the measure of each of the interior opposite angles.
110° = x + x (by exterior angle property)
110° = 2x
55° = x
Consider reason (A) statement.
A triangle with one of its angle 90°, is called a right triangle.
A and R both are correct, but the R is not an explanation of the A.
Hence, option (B) is the correct answer.