Concept:
Group behaviour often influences the effort and performance of individuals working together.
Step 1:
When people work in groups, responsibility may become distributed among members.
Step 2:
Social loafing occurs when individuals reduce their personal effort because they believe others will complete the task.
Step 3:
As group size increases, some members may contribute less while depending on the efforts of others.
Step 4:
• Somatoform tendency relates to psychological symptoms.
• Social inhibition refers to reduced performance in presence of others.
• Situationism explains behaviour based on situations.
Step 5:
Therefore, the correct answer is Social loafing.
\[
\boxed{\text{(3) Social loafing}}
\]