What is one characteristic of a sample of matter that indicates it is a pure substance? A) It can be separated using by a physical means, such as filtering. B) The components in a pure substance do not have to be in definite ratios. C) If the composition of a sample varies, the sample is a pure substance. D) If the composition of a sample is fixed, the sample is a pure substance.

Physics · Middle School · Tue Nov 03 2020

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Here, option (D) is correct. 

If the composition of a sample is fixed, the sample is a pure substance. A pure substance is a substance or compound that cannot be separated physically.  A chemical change must occur for it to be separated.