Mental stress typically arises from psychological pressures and emotions such as anxiety, frustration, and impatience.
- Joyful is a positive emotion, and it does not cause mental stress.
- Happiness is also a positive feeling and not a form of stress.
- Optimism represents a positive attitude and is generally associated with lower levels of mental stress.
However, Impatience is a state of mind where a person feels a sense of urgency or frustration, which can lead to mental stress. It is a reaction to delays or the inability to control situations, and thus, it is an example of mental stress.
Therefore, the correct answer is Impatience.