At which stage can children solve statements of propositional logic such as - "If All Humans are fish and some fish are intelligent. Are all humans intelligent"?

Option 4 : Formal Operational Stage

According to Piaget, cognitive development takes place at different rates at different stages of development. At the elementary level, there is not only an increase in children's capacity to learn but also a qualitative change in their thinking process. Piaget has classified the whole continuum into four stages to elaborate on the process of cognitive development.

• Sensory Motor Period (0-2 years) 
• Pre-operational period (2-7 years)
• Concrete operation period (7- 11 years)
• Formal operational period (11-15 years) ​

 The Formal Operational Period: Formal operational period is the fourth stage of Piaget's classification which starts at about the age of 11 years and continues till about the age of 15 years. At the stage of concrete operation (7-11 years), the child requires mainly four imconcrete operation stage: Mental representation, mainly requireslass inclusion, and Multiple classifications.  

 Characteristics of formal operational period:

• A stage of thinking about the thinking process rather than merely thinking about the context of thought. 
• A stage of applying different and flexible ways to think about ideas. 
• A stage of real versus possible. Children do not think only about concrete things but start thinking about imaginary things and possible occurrences. 
• At when elementary level children can use deductive logic, and abstract thinking while at the primary level children prefer inductive logic. 
• When children start thinking systematically and methodically.

Thus by all these references, we can consider that the formal operational stage is the stage in which a child can relate logic to this type of question" if All Humans are fish and some fish are intelligent. Are all humans intelligent?"