Which block cipher below uses a block size of 128 bits and key sizes up to 256 bits?

The choice of Twofish as the correct answer can be attributed to its specific characteristics as a block cipher. Twofish is designed to operate with a block size of 128 bits, making it suitable for various applications that require this level of granularity in data encryption. Additionally, Twofish supports key sizes of up to 256 bits, which enhances its security by providing a broader range of keys for encryption, thus making it more resilient against brute-force attacks.

In contrast, ChaCha20 is a stream cipher that operates on a different principle and does not use block sizes or key sizes in the same manner as block ciphers. Blowfish, while it does have a block size of 64 bits and supports key lengths up to 448 bits, does not meet the 128-bit block size requirement. Lastly, RC4 is also a stream cipher and does not utilize a block size at all, making it unsuitable for this question. Therefore, Twofish stands out as the only option that meets both the block size and key size specifications outlined in the question.