The color change of an indicator is used to determine ​

Whether a solution is acidic or basic can be measured on the pH scale. When universal indicator is added to a solution, the color change can indicate the approximate pH of the solution. Acids cause universal indicator solution to change from green toward red. ... Acidic solutions have a pH below 7 on the pH scale.

Explanation:

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altitude, density, pressure

air gets less dense the higher the altitude and also the air pressure is less as altitude rises.

first one is the correct answer