Answers

2014-09-13T22:42:04+05:30
Algae is used in blue and red litmus paper to find out the nature of a particular substance whether the substance is acidic or basic. They are usually prevented from decaying because if it is exposed to air it may form molds.
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2014-09-15T21:15:27+05:30
Rather hard to say without knowing the background. I'm going to assume because if they decayed, they will use up available oxygen or contaminate the sample with decomposition products.
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