Statement (a) is correct: UPI enables direct bank-to-bank transfers through mobile apps, removing the need for intermediate mobile wallets. Statement (b) is incorrect: UPI promotes digital transactions, but it will not completely replace physical currency in the near future. Statement (c) is incorrect: UPI deals with domestic payment systems and has no direct impact on FDI inflows. Statement (d) is incorrect: Direct Benefit Transfer (DBT) uses Aadhaar-linked bank accounts, not UPI, as the main mechanism for subsidy distribution.