Hello Tushar Jindal
The org will evaluate all the proposals,
The org MAY choose a proposal for an idea with only one candidate, but it won't by any means have a 100% chance of getting selected. First of all, note that the organizations usually have many more project ideas than slots they are finally given, so they can't actually fill all of them. They may have 8 great proposals, but only two students. Then, there is the quality of the proposal. If it is a weak proposal, it seems that the goals are not realistic, the student would be problematic within the community, etc. that slot can be returned, so that a better proposal can be enjoyed by another organization.
You should focus on writing a good proposal for a project you that motivates you and will enjoy doing full time during the summer, not choosing an idea exclusively based on metainformation on other proposals.