Answer:
Number of bacteria required 
Explanation:
Given -
Size of each bacterium
micrometers long
These bacteria are arranged end to end.
The size of chain to be formed is equal to
centimetres
Let us say that in forming a chain of
centimetres nearly X number of individual bacterium are required.
hence, number of bacterium required to form
centimetres chain can be represented as

Number of bacteria required 
Answer:
The invention of the electron microscope allowed them to see organelles and other structures smaller than cells. There is variation in cells, but all cells have a plasma membrane, cytoplasm, ribosomes, and DNA. These similarities show that all life on Earth has a common ancestor in the distant past
A marmoset is a member of the family of primates and are known to be one of the smallest monkey. They are measured to have a body length of 12 - 15 inches and has a mass of approximately 100 - 125 g. Comparing to monkeys, marmosets have distinct characteristics. Instead of having nails, they have claws, they tactile hair or a sensitive hair found on their wrists. They do not have wisdom teeth and the layout of their brain is primitive.
The most appropriate microscope for studying the internal parts of the cell is ELECTRON MICROSCOPE. The correct option is B.
Electron microscope, which is a compound microscope is usually used to study the internal environment of the cell because of the easiness with which one can easily distinguish the cell organelles from one another. Electron microscope gives great clarification of the cellular components and allow scientists to observe minute details about cellular structures. Electron microscope usually magnify specimens to one million times of their real sizes.