This question tests knowledge of the tools used to represent how a company is structured.
A diagram that shows the different positions within a company, along with the reporting relationships and lines of authority connecting them, from the top management down to the lowest level of staff, is called an organizational chart. It gives a visual picture of who reports to whom and how responsibility is distributed across departments and levels within the business.
The other terms describe different things. A flow chart illustrates the sequence of steps in a process or procedure, such as how an order is processed, rather than the positions held by people in a company. Span of control refers to the number of subordinates that a single supervisor or manager can effectively oversee; it is a concept related to management structure, but it is not itself a diagram. Vertical integration describes a business strategy where a company takes ownership of different stages of production or distribution, for example a manufacturer acquiring its own raw material supplier, which has nothing to do with depicting reporting positions within a single company.
Whenever a question describes a diagram of positions and reporting lines within a company, the correct term is organizational chart, not the concepts of span of control or vertical integration, which describe management ideas rather than the diagram itself.