Level balustrade should be:

In residential applications, the standard height for level balustrades is typically 36 inches above the floor level. This height is established to provide a safe barrier without feeling excessively restrictive. It is important to ensure that the height accommodates the needs across different ages and sizes of people in the household while also adhering to building codes and safety regulations designed to prevent falls.

This height is commonly accepted and recognized in various building codes across many regions, which is why it is chosen as the correct answer. While commercial applications often require higher balustrades, residential standards prioritize a balance between safety and comfort, making 36 inches the appropriate guideline.