Empirical evidence is evidence collected after observation and documentation of a pattern or a behaviour. In order to be empirical, it needs to be based on objective statements and solid proof.
So, from the list, what could be empirical evidence is:
1. a historical study showing that Indian workers were paid low wages, because a historical study is based on facts.
2. research showing that planters encouraged rivalry between workers, because a research is also based on solid proof, it isn't subjective.
The rest of the options are not objective, as they are based on personal statements and not on actual facts, and for this reason they cannot form part of empirical evidence.