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Which of the ...

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Which of the following is likely to be a pure substance?
A) A colourless liquid that boils over the range 70 $^{o}$ C to 80 $^{o}$ C.
B) A green solid which starts to melt to 80 $^{o}$ C and is completely melted at 90 $^{o}$ C.
C) A white solid which produces a chromatogram consisting of only one spot.
D) A brown liquid that is completely miscible with water.

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Solution

A substance is called a pure substance if and only if it has a fixed melting point and boiling point.
(A)Liquid has boiling point in range $70 - 80^{o} c$ .So,no fixed point -not pure.
(B)The melting point varies from $80 - 90^{o} c$ .so,not pure.
(C)Chromatogram gives only one spot-Pure substance.
(D)Brown liquid has some water in it.-impure.

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