What field in a TCP segment is used to determine if an arriving data unit exactly matches the data unit sent by the source?]

The correct answer to the following question will be "Checksum".

Explanation:

A variable that reflects the amount of several bits in a transmitted packet and is used by practitioners of IT to spot heavy-level anomalies in the transmission of data, known as Checksum.

After executing a cryptographic hashing algorithm each piece of information or a document could be allocated a value of checksum before delivery. We are relevant because we are using them to verify the authenticity of the documents.

So, it's the right answer.