Final answer:
The basic personality trait characterized by assertiveness and confident assurance is extroversion, one of the Big Five personality traits.
Step-by-step explanation:
The basic personality trait characterized by assertiveness, open expression of impulses, and confident assurance is extroversion. This trait is one of the five major dimensions of the Five Factor Model of personality, often known as the 'Big Five' personality traits. Extroversion is described as being characterized by sociability, assertiveness, excitement-seeking, and emotional expression. People high on this trait are generally outgoing, social, and enjoy being around others. This contrasts with introversion, whereby individuals have a higher need for solitude and are more reserved.