Explanation:

- Option 1: though he does not earn

- This part is grammatically correct. It introduces a contrasting idea using "though".

- Option 2: much money

- This segment is fine. "Much money" is a correct expression to describe a large amount that someone does not have.

- Option 3: He is more smarter

- This is the segment with the grammatical error. "More" and "smarter" are both comparative forms, so using both together is incorrect. It should simply be "He is smarter."

- Option 4: than his brother

- This part is grammatically correct. It properly uses "than" to compare two entities.

- He is more smarter needs correction to "He is smarter."