Final answer:
Copper is not a major element of a microbial cell; it is a micronutrient required in smaller amounts, unlike hydrogen, carbon, and oxygen which are major macronutrients.
Step-by-step explanation:
The element that is not a major element of a microbial cell is d) Copper. In microbial cells, hydrogen, carbon, and oxygen are part of the macronutrients, which account for about 99% of the cell's dry weight and are critical for the structure and function of the cell's macromolecules. Elements like copper, on the other hand, are considered micronutrients or trace elements. They are required in much smaller amounts compared to macronutrients.
Copper is involved in various enzyme functions and is essential to life, but it does not make up the core components of cells like hydrogen, carbon, and oxygen do. Hence, when listing the major elements of a microbial cell, copper should not be included as a major element.