Which of the following is the LEAST secure hashing algorithm?

SHA1 produces a 160-bit hash and is also considered weak and deprecated, but its collision vulnerabilities were demonstrated later and with greater computational effort than MD5, making it comparatively more secure than MD5.

RIPEMD (particularly RIPEMD-160) produces a 160-bit hash and was specifically designed as a more secure alternative to MD5, with no practical collision attacks demonstrated against its stronger variants, making it more secure than MD5.

MD5 (Message Digest 5) produces a 128-bit hash and is considered the least secure among the listed hashing algorithms because practical collision attacks have been demonstrated since the mid-2000s, meaning two different inputs can be engineered to produce the same hash output. MD5 is so thoroughly broken that it should never be used for security-sensitive purposes such as password storage or digital signatures, and major standards bodies have deprecated it entirely.

DES (Data Encryption Standard) is a symmetric encryption cipher, not a hashing algorithm, so it does not belong in a comparison of hashing algorithm security; while DES is considered insecure for encryption, it is categorically different from a hash function.