Q$6$ TCP SYN $($b$).$ What is it in this TCP segment that identifies the segment as a SYN segment?

The SYN bit is set to $1$ in the "Flag" field in the TCP header.

The first segment in a TCP connection is always a SYN segment, so this segment is recognized as a SYN segment even though there is no explicit marking in this segment to indicate it is a SYN segment.

The TCP options field in the TCP header contains the ASCII characters $"$SYN$",$ indicating that this is a SYN segment

The initial sequence number used is the sum of the ASCII values of the characters $\text{'}$S$\text{'},\text{'}$Y$\text{'},$ and $\text{'}$N$\text{'},$ indicating that this is a SYN segment.