Final answer:
The concept that increases the likelihood of friendship based on frequent contact is known as proximity, therefore Sam is most likely to become friends with his next door neighbor.
Step-by-step explanation:
The concept that suggests your roommate is more likely to become your friend than a person ten blocks away is known as proximity. This concept is supported by decades of research indicating that we are more inclined to forge friendships with those we see more frequently. This means that among the options provided, Sam is most likely to become friends with a. his next door neighbor. Proximity facilitates regular contact and thereby increases the opportunity to develop a friendship.
Another key factor in forming relationships is similarity. We tend to form closer relationships with people who share similar backgrounds, attitudes, and lifestyles. This is because sharing common interests and values makes it easier to connect and engage in activities together.