Final answer:
Children acquire conservation skills during the concrete operational stage of cognitive development, which occurs from about 7 to 11 years old, enabling them to understand that properties such as mass, volume, and number remain the same even when appearances change. Most children successfully acquire conservation skills during the concrete operational stage of cognitive development, which is option (c).
Step-by-step explanation:
Most children successfully acquire conservation skills during the concrete operational stage of cognitive development, which is option (c). Jean Piaget identified this stage as the third in his theory of cognitive development, occurring approximately from 7 to 11 years old. During the concrete operational stage, children develop the ability to think logically about concrete events. They gain a better understanding of concepts like the conservation of mass, volume, and number, recognizing that these properties do not change even when the appearance of an object is altered.
For instance, in the example of Keiko and Kenny and the pizza, Keiko understands that Kenny's pizza slice, although cut into more pieces, is not larger in quantity than her single slice because the amount of pizza has not actually changed. This understanding reflects a grasp of conservation, indicative of the cognitive abilities developed in the concrete operational stage.