In their marital relationship, Sylvia most enjoys conversation that explores relationships, whereas her husband most enjoys working side-by-side on extended projects. Their unique activity preferences best illustrate a difference in .

Social Connectedness.

Explanation:

Social connectedness can be defined as a measure of people coming together and interacting with each other. Humans are social beings hence they are prone to make connections with friends and family, and society.

In the given case, Sylvia is more socially connected as she enjoys having conversations that explore relationships, and on the other hand, her husband mostly enjoys working on extended projects. It is because of the difference in social connectedness.

So, the correct answer is social connectedness.