Question

Phenolphthalein is used to test rhe presence of carbon dioxide in exhaled air

Answer 1

Explanation:

Air is sucked in by mouth, through the tube at the centre.

Atmospheric air rushes into the flask, bubbling through the lime water.

Air cannot get in through B as that end is closed.

Then open end B and close A, and breath out the air. The exhaled air cannot escape out of A. So, it has to pass through the limewater.

The lime water in b turns milky, much faster than in A. This proves the much higher percentage of carbon dioxide in exhaled air than inhaled air.