The answer is extroversion.
Neuroticism refers to the tendency to experience negative emotions such as anxiety, anger, or depression. Someone who is quiet, reserved, and withdrawn does not necessarily score low on neuroticism; they might still experience these negative emotions.
Agreeableness involves being compassionate, cooperative, and friendly. A person who is quiet, reserved, and withdrawn might still be agreeable, as these traits do not directly relate to social interaction levels.
Openness to experience involves being imaginative, curious, and open to new experiences. Being quiet, reserved, and withdrawn does not necessarily indicate a low score on openness, as these traits are more about social interaction than curiosity or imagination.
Extroversion is characterized by sociability, talkativeness, and assertiveness. Someone who is quiet, reserved, and withdrawn would score low on extroversion, as these traits are the opposite of what defines an extroverted personality.