"An eight years old child crawls like his younger infant brother” is an example of

Defense mechanisms are unconscious psychological strategies used by individuals to protect themselves from anxiety, internal conflicts, or unacceptable thoughts and feelings. 

Key Points

• Regression is demonstrated when an eight-year-old child begins to crawl like his infant brother. In this case, the child is reverting to an earlier developmental stage where crawling symbolized comfort and safety.
• This often happens when the child feels insecure, jealous, or anxious, such as after the arrival of a new sibling.
• By adopting infant-like behavior, the child unconsciously seeks attention or attempts to cope with emotional stress by returning to a time when they felt more secure and nurtured.

Hint

• Repression involves unconsciously blocking painful thoughts or memories from awareness, not physically acting younger.
• Rationalization is when a person justifies unacceptable behavior with logical but false explanations, which is not happening here.
• Compensation occurs when someone covers up real or perceived weaknesses by emphasizing strengths in another area, which does not match the behavior of crawling like an infant.

Hence, the correct answer is regression.