in this form of encryption algorithm, every Individual block contains 64-bit data, and three keys are used, where each key consists of 56 bits. Which is this encryption algorithm?

IDEA (International Data Encryption Algorithm) uses a single 128-bit key rather than three 56-bit keys, so it does not match the key structure described.

Triple DES (3DES) applies the DES cipher three times sequentially using three independent 56-bit keys, yielding an effective key length of 168 bits, and processes plaintext in fixed 64-bit blocks. This dual characteristic - three 56-bit keys and 64-bit block size - precisely matches the description in the question and distinguishes 3DES from all other listed algorithms.

MD5 is a cryptographic hash function used for message integrity verification, not a block cipher encryption algorithm, and does not use 56-bit keys or encrypt plaintext data blocks.

AES operates on 128-bit blocks and uses key sizes of 128, 192, or 256 bits - not three 56-bit keys or 64-bit blocks as described in the question.