Final answer:
A 5-year-old conversing with an imaginary friend demonstrates the preoperational stage according to Piaget, which is characteristic of ages 2 to 7 and includes symbolic play and egocentric thinking.
Step-by-step explanation:
A 5-year-old who has an imaginary friend with whom he converses frequently is displaying characteristics consistent with Piaget's preoperational stage. According to Jean Piaget's theory of cognitive development, the preoperational stage typically occurs between the ages of 2 and 7. Children in this stage engage in symbolic play and may have difficulties understanding the perspective of others, demonstrating tendencies like egocentrism. They lack the ability to perform operations, which refers to logical manipulation of information, and do not understand the principle of conservation. This developmental stage is marked by growth in the use of language and increasing ability to represent objects with words and images.