Questions: detects the presence of the enzyme catalase by noting whether bubbles are released when Hydrogen peroxide is added to a culture example.

The answer is the third one: catalyst test.

Explanation for each option:

1. Direct microscopic cell count: This method involves counting the number of cells in a sample using a microscope. It does not involve adding hydrogen peroxide or detecting enzyme activity, so it is incorrect.

2. Viable cell count: This method estimates the number of living cells in a sample by culturing them and counting the colonies that form. It does not involve adding hydrogen peroxide or detecting enzyme activity, so it is incorrect.

3. Catalyst test: This is the correct answer. The catalyst test, often referred to as the catalase test, detects the presence of the enzyme catalase. When hydrogen peroxide is added to a culture, the presence of catalase is indicated by the release of oxygen bubbles.

In summary, the catalyst test is used to detect the presence of the enzyme catalase by observing bubble formation when hydrogen peroxide is added.