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A student takes four samples of a white crystalline solid and places each in a well plate. On top of each sample, she carefully places 20 drops of clear mystery liquids A, B, C and D. Her results for each well are as follows:

Liquid A: The solid dissolves quickly.

Liquid B: The solid appears unchanged.

Liquid C: A brownish colored liquid is produced.

Liquid D: Fizzing occurs and the well becomes warmer.



In which well does a PHYSICAL change occur?