Question

Why should the level of water in the beaker be above the level of the stem of the inverted funnel?

Answer 1

Now, fill a test tube with pond water and invert it over the stem of the funnel. ... the level of the beaker of water in the beaker should be above the level of the stem of the inverted funnel.

Answer 2

Answer:

In the experiment to prove $O_{2}$ is released during photosynthesis, the water level kept in the beaker is 3/4th. This is because a test tube containing pond water must also be kept in the beaker along with the Hydrilla plant. If the level of water is more than this the water of the tube and plant will not get a place to accumulate themselves.

The level of the stem of the inverted funnel is less than the water level in the beaker in order to maintain the jet of the funnel remains inside the tube in a vertical position.

Explanation:

Basically, the water level would fall down if the neck/stem of the funnel since it is does not have water. If water is there, neither will the water level (jet) do down, nor will any external gases interefere with the outcome of the experiment. Otherwise, other gases will move into the stem of the inverted funnel and into the inverted test tube