The purpose of setting up Small Finance Banks (SFBs) in India is captured in options 1 and 2.

In option 1, "To supply credit to small business units", this is indeed a main focus of SFBs. These banks are established to help small businesses access credit facilities, boosting their operational capabilities and growth.

Option 2, "To supply credit to small and marginal farmers", is also correct. SFBs aim to enhance financial inclusion by providing banking services to the underprivileged and unbanked sections of society, including small and marginal farmers.

Option 3, "To encourage young entrepreneurs to set up business particularly in rural areas" is not necessarily a primary objective of SFBs. While they may indirectly support young entrepreneurs by providing credit which may help to establish businesses, it is not their direct purpose. Therefore, option 1, which comprises only options 1 and 2, is the correct answer.

Options 2, 3, and 4, which include option 3, are thus not the correct choices specifically because they miss the essential aim of SFBs.