Thanks Ishika :) See, there is no exact number of contributions to be on safer side, I have seen folks who submitted a lot of PRs but were not selected due to compromising quality(there may be other reasons idk). it totally depends upon the complexity of the issue and the codebase, some issues could be solved within two-three days, while some may take one-two weeks. Quality is the thing that can set you apart, so minimum contribution is one and maximum it could be any number.

Thanks for clarifying