Four-year-old christopher begins to use primitive reasoning and wants to know the answers to all sorts of questions. he is in what substage of preoperational thought?

He is in "intuitive thought".

A sub-stage in Piaget's Preoperational stage is Intuitive thought sub-stage, which traverses ages 4-7 years. Youngsters in this stage of advancement learn by making inquiries, for example, "Why?" and "How?" Piaget named this "intuitive thought" since he trusted that kids at this stage have a tendency to be so sure of their insight and understanding that they are unconscious of how they picked up this information in the first place.