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Give brief answers to the following question:
 
A group of students took an old shoebox and covered it with a black paper from all sides. They fixed a source of light (a torch) at one end of the box by making a hole in it and made another hole on the other side to view the light. They placed a milk sample contained in a beaker/tumbler in the box as shown in the below figure. They were amazed to see that milk taken in the tumbler was illuminated. They tried the same activity by taking a salt solution but found that light simply passed through it?
 
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(a). Explain why the milk sample was illuminated. Name the phenomenon involved.

(b). Same results were not observed with a salt solution. Explain.

(c). Can you suggest two more solutions which would show the same effect as shown by the milk solution?