Question

what is the reason why the test tube was covered with the thumb and inverted to test on the funnel

Answer 1

Answer:

The gas bubbles may be observed from the ends of the Hydrilla branches kept under the glass funnel in the beaker. These gas bubbles are accumulated in the end of the test tube inverted over the end of the funnel, and the water within the tube goes downward. On test the gas is to be proved oxygen.