Steam engine facts — choose the correct statement: Which of the following statements about steam engines is correct?

Introduction / Context:
Objective questions often test common misconceptions about engine layout, operating pressure ranges, and condensing practice. Here we examine three assertions and identify whether any is correct.

Given Data / Assumptions:

• Comparison between horizontal and vertical reciprocating steam engines.
• Possibility of sub-atmospheric cylinder pressure in condensing engines.
• Use of compounding (multi-stage expansion) with or without condensers.

Concept / Approach:
We evaluate each statement against standard engineering practice:
1) Layout: Vertical engines save floor area compared with horizontal engines of similar output, so a horizontal engine usually requires more floor space, not less.
2) Cylinder pressure: Condensing engines commonly exhaust to a condenser under vacuum, so cylinder pressure can fall below atmospheric near exhaust; the claim that it is not allowed is false.
3) Compounding: Many compound engines are specifically paired with condensers to exploit larger expansion ratios efficiently; the blanket statement that they are generally non-condensing is false.

Step-by-Step Solution:
Check (a): false; vertical layout is more compact in plan area.Check (b): false; condensing produces sub-atmospheric back pressure.Check (c): false; compounding and condensing are often combined.Therefore none of the listed statements is correct → choose “none of these”.

Verification / Alternative check:
Historical plant layouts and textbooks consistently cite vertical engines for reduced footprint and condensing for efficiency gains through lowered back pressure.

Why Other Options Are Wrong:
Option (d) “all of the above” cannot be true because each individual statement is false.

Options (a), (b), (c) are individually refuted by standard practice.

Common Pitfalls:
Applying internal-combustion engine intuition to steam engines; forgetting the effect of condensers on exhaust pressure and the typical pairing of compounding with condensing.

Final Answer:
none of these