In the following item, a technical passage about a device that heats fluids without an electrical element is jumbled. The passage consists of six sentences with S1 and S6 fixed. The four middle sentences labelled P, Q, R and S are given in a mixed order. Read the passage carefully and choose the option that gives the correct sequence of P, Q, R and S between S1 and S6. S1: A single device can heat fluids without requiring an electrical element. S6: Because there is no electrical element, there is no risk of fire, so the system is suitable for dangerous environments. P: A heat exchanger transfers heat from the central cavity to an air heater, a water heater or an industrial processor. Q: It has a container like the crankcase of a car's engine, which contains the fluid to be heated. R: Compression and friction at the nozzles heat the fluid so that the temperature in the central cavity rises steadily. S: A motor and pulley inside the container turn a rotor wheel, which in turn forces the fluid again and again through narrow nozzles into a central cavity. The proper sequence should be

Introduction / Context:
This passage describes a mechanical device that can heat fluids without using any electrical heating element. The first and last sentences are fixed and state the overall capability and safety of the system. The middle sentences explain how the device is built and how it works. Your task is to arrange these middle sentences in a logical, step by step description of structure and operation.

Given Data / Assumptions:

• S1: A single device can heat fluids without an electrical element.
• S6: There is no risk of fire and the system suits dangerous environments.
• Q: The device has a container similar to a crankcase that contains the fluid.
• S: Inside the container, a motor and pulley turn a rotor wheel that pushes fluid repeatedly through nozzles into a central cavity.
• R: Compression and friction at the nozzles heat the fluid, raising the temperature in the central cavity.
• P: A heat exchanger transfers heat from the central cavity to different types of heaters or industrial processors.
• We assume the passage will first describe the physical structure, then the motion of fluid, then the heating mechanism, and finally the heat transfer to other systems.

Concept / Approach:
To order these sentences:

• First identify the basic structure: the container and what it holds.
• Next describe the internal moving parts and how they move the fluid.
• Then explain how that motion produces heat.
• Finally, describe how the generated heat is used via a heat exchanger.

A clear mechanical process must go from static structure to dynamic action to practical output.

Step-by-Step Solution:
Step 1: After S1 states that the device heats fluids, the reader needs to know what the device physically looks like. Sentence Q provides this: “It has a container like the crankcase of a car's engine, which contains the fluid to be heated.” So Q follows S1. Step 2: Once the container is introduced, the next logical step is to describe the moving parts inside it. Sentence S does this: “A motor and pulley inside the container turn a rotor wheel, which in turn forces the fluid again and again through narrow nozzles into a central cavity.” Thus S should follow Q. Step 3: We now know that fluid is forced through nozzles into a central cavity. The next question is how heat is generated. Sentence R explains that “Compression and friction at the nozzles heat the fluid so that the temperature in the central cavity rises steadily.” Therefore R comes after S. Step 4: After the fluid in the central cavity is heated, the device must transfer this heat to useful applications. Sentence P explains that a heat exchanger transfers heat from the central cavity to an air heater, water heater or industrial processor. So P logically follows R. Step 5: With Q S R P in place, S6 then remarks that the absence of an electrical element eliminates fire risk, which concludes the description.

Verification / Alternative check:
Reading S1, Q, S, R, P and S6 in order, the explanation is clear: structure, motion, heat generation and heat utilisation, followed by a conclusion about safety. At no point does the description jump backward or leave out an essential step. Each sentence answers a new “what happens next” question, so the sequence is verified.

Why Other Options Are Wrong:
R P S Q: This begins with heating and heat transfer before even mentioning the container or how the fluid is moved, which is confusing and incomplete.
S P Q R: Here the fluid motion is described before the container is introduced, and heat transfer is mentioned before the heating mechanism is explained, which disrupts the logical order of explanation.
S R P Q and other mixed orders similarly put dynamic or outcome related details before basic structural information, making it hard for the reader to visualise the device properly.

Common Pitfalls:
Students sometimes focus on the most technical sounding sentence and place it first, rather than starting with basic structure. Another frequent mistake is to ignore the implied sequence of operations inherent in mechanical descriptions. To avoid these mistakes, always reconstruct the process in your mind, step by step, and then assign sentences to those steps in order: physical arrangement, movement, effect, and use.

Final Answer:
The correct sequence is Q S R P, so the correct option is “Q S R P”.