P-Q (Product–Quantity) Analysis is the classical starting point for deciding what kind of facility and plant layout suits a given manufacturing situation. The plot places Production Quantity on one axis and Product Variety on the other, so a single chart captures the fundamental trade-off every plant faces: the more different products you make, the fewer of each you typically produce, and vice-versa.

Reading the plot from one extreme to the other tells you which layout is economical:

• High quantity, low variety → a product (line) layout / flow production, where machines are arranged in the fixed sequence of operations (e.g., automobile assembly).
• Low quantity, high variety → a process (functional) layout / job shop, where similar machines are grouped together and each job follows its own route (e.g., a general machine shop).
• Intermediate quantity and variety → batch production or cellular (group technology) layout, a compromise that balances flexibility and flow.

This is why the correct choice is the Production quantity vs. product variety plot — these are precisely the two decision variables that govern layout selection.

The other choices fail because they mix in variables that do not drive the layout decision directly. A plot using product cost (whether against variety or quantity) treats cost as an input, but cost is actually an outcome of the layout chosen, not the criterion used to choose it. The wording production mass instead of production quantity is non-standard terminology and, in any case, still misses that the recognised industrial tool is specifically the quantity-versus-variety (P-Q) chart.