The question below consists of a set of four labelled sentences about crude mineral oil and hydrocarbons. Out of the four options given, select the most logical order of the labels P, Q, R and S to form a coherent paragraph.

Introduction / Context:
This sentence arrangement question deals with crude mineral oil and hydrocarbons. You are given four labelled sentences P, Q, R and S, and you must pick the order that produces a clear, logically organised paragraph. Such questions test your ability to identify introductions, explanations, and examples in a scientific description.

Given Data / Assumptions:

• Q: Crude mineral oil comes out of the earth as a thick brown or black liquid with a strong smell.
• R: It is a complex mixture of many different substances, each with its own individual qualities.
• P: Most of them are combinations of hydrogen and carbon in varying proportions.
• S: Such hydrocarbons are also found in other forms such as bitumen, asphalt and natural gas.
• We must choose one order from QPRS, PQRS, PQSR, QRPS.

Concept / Approach:
A good explanatory paragraph typically begins by introducing the main subject, then describing its nature, and finally giving more specific details and related examples. Q introduces crude mineral oil directly and is the natural starting point. R explains that this oil is a complex mixture of many substances. P then identifies most of these substances as combinations of hydrogen and carbon. S finally mentions where similar hydrocarbons are found, giving additional examples.

Step-by-Step Solution:
Step 1: Choose the introductory sentence. Q clearly introduces crude mineral oil, its appearance, and smell, so it should come first.Step 2: Look for the sentence that explains “it”. R begins with “It is a complex mixture…”, clearly referring back to crude mineral oil in Q, making QR a natural pair.Step 3: Next, identify what the mixture consists of. P states that most of them are combinations of hydrogen and carbon, specifying the composition of the substances mentioned in R.Step 4: Finally, S uses “Such hydrocarbons” to connect back to the hydrogen and carbon combinations in P and then shows where similar hydrocarbons are found, such as bitumen, asphalt and natural gas.Thus, the logical order is Q → R → P → S, corresponding to option QRPS.

Verification / Alternative check:
Read QRPS as a continuous paragraph: “Crude mineral oil comes out of the earth as a thick brown or black liquid with a strong smell. It is a complex mixture of many different substances, each with its own individual qualities. Most of them are combinations of hydrogen and carbon in varying proportions. Such hydrocarbons are also found in other forms such as bitumen, asphalt and natural gas.” This flows smoothly from introduction to composition to related examples.

Why Other Options Are Wrong:
In QPRS, P directly follows Q, skipping the important explanation in R that crude oil is a complex mixture; this makes the reference “Most of them” in P unclear. In PQRS and PQSR, starting with P is problematic because P speaks of “Most of them” without first telling us what “them” refers to. Only Q gives the subject (crude mineral oil) that the pronouns in later sentences can refer back to logically.

Common Pitfalls:
Students sometimes match sentences just on the basis of pronouns like “It” or “Such”, without considering whether all references are fully clear. Always ensure that every pronoun has a clear, previously mentioned noun to refer to. When you do this here, Q must be first, R must follow to explain “It”, and P and S flow naturally afterwards.

Final Answer:
The most logical order of the labelled sentences is QRPS.