Which of the following is NOT one of Piaget's stages of cognitive development?

The correct answer is identified as "Operational" because this term does not specifically refer to any of the recognized stages in Piaget's theory of cognitive development. Jean Piaget proposed four distinct stages through which children progress as they develop cognitive abilities: the sensorimotor stage, the preoperational stage, the concrete operational stage, and the formal operational stage.

The terms "preoperational," "concrete operational," and "formal operational" are all accurate descriptors of Piaget's stages. The preoperational stage spans roughly from ages 2 to 7 and is characterized by symbolic thinking and egocentrism. The concrete operational stage, emerging from about ages 7 to 11, involves the development of logical thought about concrete objects and events. The formal operational stage, beginning around age 12 and continuing into adulthood, is marked by the ability to think abstractly and engage in systematic planning and problem-solving.

"Operational" alone lacks the specific context provided by Piaget's nomenclature and does not represent a standalone stage as per his framework.