Here it is mentioned that the alpha can be negative, and in Q4 the correct answer is alpha must be +ve, can someone explain why it is the case, there is nothing mentioned about best/better solution in Q4 so why alphs must be +ve ?
It explains what a negative alpha would do and thus why it does not make sense to have a negative value. You are never interested to promote overfitting. In practice, a negative value would raise an error in scikit-learn.