<h2>
Answer:</h2>
Option: d is the correct answer.
d. An angle is obtuse if and only if its measure is greater than 180°
<h2>
Step-by-step explanation:</h2>
<u>Acute angle--</u>
An angle is acute if and only if the measure of the angle is strictly less than 90 degree.
<u>Right angle--</u>
An angle is right angle if and only if the measure of the angle is exactly equal to 90 degree.
<u>Obtuse angle--</u>
An angle is said to be obtuse if and only if the measure of the angle is strictly greater than 90 degree and strictly less than 180 degree.
<u>Congruent angles--</u>
Two angles are said to be congruent if and only if both the angles have the same measure.
Hence, the biconditional which is NOT a good definition is:
Option: d
