An unarmed 18-year-old African-American man was on his way to college when he engaged in an altercation with a police officer. The ending result was the police officer shot and killed him. Sean is a 19-year-old African-American man who is disgusted about what just took place in his neighborhood. He decides to show his frustration by joining in riots taking place in his neighborhood. Sean is in Piaget's stage of cognitive development.

The correct answer is - formal operational.

Explanation:

According to the Piaget's theory of cognitive development Sean is showing formal operational stage which is characterized by the creating and changing the hypothesis and ideas in their brains and test them without any prior knowledge or evidence.

In this case Sean made his mind to participate in riots to show is frustration without knowing the cause of altercation with a police officer, so it is the cognitive development's formal operational stage.

Thus, the correct answer is - formal operational.