While judging a personality pageant, raters gave high scores to contestants who were already famous because of their presence in popular T.V. serials or advertisements and tended to give low scores to those who were not so popular. This phenomenon is called

The correct option is Halo effect.

Step-by-step explanation:

1. Understanding the Situation: In the given scenario, raters are judging contestants in a personality pageant. Instead of evaluating the contestants solely based on their performance in the pageant, the raters are influenced by their pre-existing knowledge of the contestants' fame (their presence in popular T.V. serials or advertisements). Raters gave higher scores to those who were already popular and lower scores to those who were not.

2. Defining the Concept: The Halo effect is a cognitive bias where our overall impression of a person (in this case, their fame and popularity from T.V. or advertisements) influences how we feel and think about their character or other specific traits (in this case, their performance in the personality pageant). Because they are viewed positively in one area (fame), this positive impression "spills over" and biases the raters to judge their personality pageant performance more favorably.

3. Analyzing the Other Options:
- Recency effect: The tendency to recall or be influenced by the most recently presented information or experiences.
- Primacy effect: The tendency to recall or be influenced by the information presented first.
- Rosenthal effect (or Pygmalion effect): The phenomenon where higher expectations lead to an increase in performance.
None of these options describe the spillover of a general impression or a single trait (fame) onto other unrelated ratings as accurately as the Halo effect.