Final answer:
In Piaget's pre-operational stage, a child is unable to carry out operations, which are reversible mental actions. This is because they have not mastered the concept of conservation, unlike children in the concrete operational stage who are capable of logical thinking about concrete events and understand reversibility.
Step-by-step explanation:
According to Piaget's pre-operational stage, a child does not yet perform operations, which are defined as reversible mental actions. During the pre-operational stage, which spans from approximately 2 to 7 years old, children can use symbols to represent words, images, and ideas, leading to behaviors such as pretend play. However, they lack the ability to perform mental operations because they have not yet developed an understanding of concepts like conservation, the idea that the quantity of something remains the same despite changes in its form or appearance.
In contrast, children in the later concrete operational stage (from about 7 to 11 years old) are capable of logical thought about concrete events and comprehend the principle of reversibility. They understand transformations and mathematical operations such as the relationship between addition and subtraction or multiplication and division.