Correct option is B
The activity that is not effective in developing appreciation for mathematics among children is option (b). Praising only the student with the highest marks creates unhealthy competition, potentially demotivating others and narrowly focusing on grades rather than fostering a genuine love for math. Options (a), (c), and (d) encourage hands-on exploration, provide historical context, and engage students in problem-solving, making them more effective methods to develop math appreciation.