The correct answer is option (E):
Necessary
The passage likely discusses something that is required or essential for a particular purpose. The word "necessary" means something that is needed or required. Let's consider the other options to understand why "necessary" is the best fit.
Dispensable, inessential, and perfunctory all imply that something is not essential, can be done without, or is done with minimal effort and without real care. These words suggest a lack of importance or a lower level of requirement.
Mandatory means something that is commanded or required, but it often carries a stronger sense of obligation or legal requirement than simply being "necessary." While a mandatory action is certainly necessary, "necessary" is a more general term for something that is needed for a particular outcome or condition.
Without the full context of the passage, it's difficult to be absolutely certain. However, if the passage is describing a component, step, or action that is crucial for a process, system, or achievement, then "necessary" would be the most appropriate word to convey that it is needed and cannot be omitted without consequence. For example, if the passage states that "Oxygen is 48 for human survival," then "necessary" is the only word that fits logically. Similarly, if it talks about a specific step in a procedure being "48 to complete the task," then "necessary" indicates its importance.