In this one word substitution question, you must choose the single word that best expresses the meaning of the given definition: "A substance easily evaporated at normal temperatures." Which of the following words correctly matches this definition?

Introduction / Context:
This question tests your knowledge of scientific and general English vocabulary through one word substitution. The given definition describes a specific physical property of substances, namely how easily they evaporate at normal temperatures. Understanding such terms is useful not only for language exams but also for science and engineering studies, because many texts use this word to describe chemicals and fuels.

Given Data / Assumptions:

• The definition is: A substance easily evaporated at normal temperatures.
• The options are Volatile, Steadfast, Enduring and Definite.
• The correct word must describe the physical behaviour of a substance that readily turns from liquid to gas.
• The other options describe human qualities or abstract characteristics, not evaporation.

Concept / Approach:
In chemistry and everyday English, the word volatile is used to describe liquids that evaporate readily at normal temperatures and pressures, such as petrol or alcohol. It is also used metaphorically to describe situations or personalities that change quickly or become dangerous suddenly. The other options refer to stability of character (steadfast, enduring) or clarity of meaning (definite) and do not relate to evaporation. Matching the scientific definition to the correct term allows you to eliminate the unrelated options easily.

Step-by-Step Solution:
Step 1: Focus on the key phrase in the definition: easily evaporated at normal temperatures. Step 2: Recall that Volatile, in scientific context, means a substance that readily vaporises, often giving strong fumes. Step 3: Check usage: phrases like volatile liquids or volatile organic compounds refer specifically to easily evaporated substances. Step 4: Consider Steadfast, which means firm and unwavering, describing loyalty or support, not physical evaporation. Step 5: Consider Enduring and Definite. Enduring means lasting for a long time, and definite means clearly stated or decided. Neither refers to a substance changing from liquid to gas. Therefore volatile is the correct choice.

Verification / Alternative check:
Imagine a laboratory sign that warns about a chemical. It might say Handle with care, this is a highly volatile liquid. This sentence makes sense because volatile indicates a liquid that forms vapour easily, possibly leading to fire or inhalation risk. In contrast, if the sign used steadfast or enduring, it would not relate to safety at all. Using definite in this context would also be meaningless. Checking real life phrases in your mind is a practical way to confirm that volatile is the word that matches the given definition.

Why Other Options Are Wrong:
Steadfast is a character trait meaning firm, loyal and reliable, as in steadfast friend. Enduring means lasting or continuing over time, as in an enduring legacy. Definite refers to something clearly defined or decided, such as a definite plan. None of these terms are used to describe the ease with which a substance evaporates. They belong to completely different meaning areas and therefore cannot be the one word substitution for the provided scientific definition.

Common Pitfalls:
Some candidates may have seen volatile used for unstable political situations or emotional people and may not immediately recall its original scientific sense. It is important to understand that many English words have both literal and figurative meanings. In exams, the definition often points clearly to one of these senses. Another pitfall is choosing enduring because it sounds technical, but a substance that is enduring is long lasting, not easily evaporated. Careful reading of the definition word by word will help you connect it to the right concept and avoid such traps.

Final Answer:
The correct one word substitution for A substance easily evaporated at normal temperatures is Volatile.