Which statement correctly describes a 'basis' in reactor calculations?

• A. A basis is a fixed reference temperature for calculations.
• B. A basis specifies the reactor pressure limit.
• C. A basis defines the reactor shape and size.
• D. A basis fixes a reference flow rate or amount (such as 1 hour, 1 mole, or 100 mol) to express conversions and rates.

Answer: (D)

In reactor calculations, a basis is a fixed reference quantity—an amount of feed or a time—that you use to express conversions and rates. By choosing something like 1 mole of feed, 100 moles, or a per-hour basis, all conversions, yields, and rate expressions are scaled to that reference so quantities like molar flow rates and concentrations stay consistent and comparable. This makes material balances and design calculations workable, because you can relate what happens inside the reactor to a well-defined starting amount.

That’s why the statement describing fixing a reference flow rate or amount to express conversions and rates is the best fit. The other ideas describe temperature references, pressure limits, or physical size, which are important in reactor design but do not capture what a basis is in the context of expressing conversions and rates.