Wanting to eat a piece of chocolate cake but not wanting to gain weight is an example of an type of conflict

The right answer is the approach-avoidance conflict.

A conflict refers to the situation in which an individual is exposed to cognitive and motivational tendencies of opposite meaning.

From the perspective of scientific psychology, there are three types of conflict:
*Approach-approach conflicts: There are two non-simultaneously feasible trends towards two incompatible objects or goals.
*Avoidance-Avoidance Conflicts: The two incompatible tendencies lead the individual to flee two distinct objects or goals.
*Approach-avoidance conflicts: the same object (chocolate) or goal (losing weight) simultaneously creates a tendency to approach and a tendency to avoid.