The correct answer is option 2.In the congestion avoidance algorithm, the size of the congestion window increases Additively.?Hence the correct answer is Additivity.Additional Information To avoid congestion, the sender TCP has two strategies: one is a slow start and additive increase, and the second is called multiplicative decrease.?Additive Increase:To avoid congestion before it happens, one must slow down this exponential growth. After the size reaches the thresholds, the size is increased by one segment for each acknowledgment even if an acknowledgment is for several segments.Multiplicative Decrease:If congestion occurs, the congestion window size must be decreased. The only way the sender can guess that congestion has occurred is through a lost segment. If the sender does not receive an acknowledgment for a segment before its retransmission timer has matured, it assumes that there is congestion.