Answer: preoperational
Step-by-step explanation:
The concept of preoperational condition was given by Jean Piaget in his theory. It suggests that because of egocentric and intuitive nature a child cannot develop a logical reasoning and is not capable of doing mental tasks. He suggested that children in the age of 6 to 7 are in the preoperational stage.
According to the given situation the child has given wrong answer as the fat and small container can have larger volume and it can be filled with more sand than thin and tall container this is indicative of the fact that child is at the stage of preoperational cognitive development.