Step 1: Meaning of the term:
'Verfremdung' means making something strange or unfamiliar. In theatre it means making familiar events look strange, so that the audience stops taking them for granted.
Step 2: What Brecht wanted from the audience.
In epic theatre Brecht wanted spectators who think and decide, and not spectators who only cry or laugh with the characters. To get this, he used narrators, bare lighting, visible lamps and acting where the actor shows the character from outside. All of these keep a gap between the viewer and the story.
Step 3: Test each option against this aim.
Option 1 (emotional immersion) and option 2 (audience identification) are the opposite of a gap, since they pull the viewer into the story. Option 4 (realism) tries to hide the stage tricks, but Brecht made them visible. Option 3 (detachment and critical thinking) fits the aim of the gap.
Step 4: Conclusion.
Only option 3 describes what the alienation effect is for.
Final Answer:
Brecht used the alienation effect to create distance and make people think. The answer is option 3.
\[ \boxed{\text{Option 3}} \]