Which is not a mixture? 1. sea water 2. a glass of kool-aid 3. sodium chloride 4. a jar filled with rocks and sand?

Sodium chloride, NaCl.

Explanation:

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In this case, sodium chloride whose formula is NaCl is not a mixture since it is a pure substance formed by the chemical bonding between sodium and chlorine via an ionic bond. This is substantiated throughout the fact that sea water is an homogeneous mixture as well as the glass of kool-aid. On the flip side, a jar filled with rocks and sand is an heterogeneous mixture as you are able to notice the difference between the rocks and the sand.

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