In the following question, out of the four alternatives, select the word that is opposite in meaning to the given word. Phlegmatic.

Introduction / Context:
This vocabulary question asks for the antonym of “phlegmatic”. Exam setters frequently use temperament words like “phlegmatic”, “sanguine”, “melancholic” and “choleric” to test sophisticated vocabulary. “Phlegmatic” generally describes a calm, unemotional and slow-to-react person. To answer correctly, you must identify which option expresses the opposite quality, that is, someone who is highly emotional, energetic or passionate in response to situations.

Given Data / Assumptions:

The target word is “phlegmatic”.
The options are “ardent”, “indifferent”, “prohibit” and “merciless”.
The task is to find the opposite in meaning, not a synonym.
We assume standard psychological or personality usage of “phlegmatic”.

Concept / Approach:
“Phlegmatic” refers to a person who remains calm, unemotional, and rarely shows excitement or anger. Such people are often described as slow to react emotionally. The opposite temperament would be someone who responds with strong feelings, enthusiasm or passion. “Ardent” is an adjective meaning passionate, eager or intensely enthusiastic. Therefore, “ardent” stands as a natural antonym to “phlegmatic”. The other options do not describe temperament in a directly opposite way and thus cannot serve as antonyms in this question.

Step-by-Step Solution:
Step 1: Translate “phlegmatic” into simpler words: calm, unemotional, sluggish in showing feelings. Step 2: Think about what the opposite personality type would be: highly emotional, passionate, strongly enthusiastic. Step 3: Look at the options. “Ardent” means passionate, intensely eager or enthusiastic. Step 4: “Indifferent” means not concerned or not interested, which is closer to emotional detachment, not the opposite of calmness. Step 5: “Prohibit” is a verb meaning to forbid, and cannot describe a person's temperament. Step 6: “Merciless” means without mercy or cruel; that talks about degree of compassion, not emotional energy or slowness. Step 7: Therefore, “ardent” is the most suitable antonym of “phlegmatic”.

Verification / Alternative check:
Use the words in simple personality descriptions. “She has a phlegmatic nature” suggests she stays calm and unemotional. “She has an ardent nature” suggests she is full of passion, energy and strong feelings. These descriptions are opposite in emotional intensity. By contrast, “He is indifferent” means he does not care, which may overlap slightly with emotional flatness, but not in a directly opposite way. Also, “merciless” and “prohibit” do not describe personality in terms of emotional intensity, which confirms that they are irrelevant as antonyms here.

Why Other Options Are Wrong:
Indifferent: This means uncaring or having no particular interest. A phlegmatic person may appear indifferent, but the terms are not perfect opposites; they both suggest low emotional response in different ways, so “indifferent” is not the contrasting extreme we want.
Prohibit: This is a verb meaning to forbid or prevent, and cannot serve as an opposite for a temperament adjective like “phlegmatic”.
Merciless: This means cruel or without pity and relates more to moral character than to emotional energy. A person can be merciless and still be either very emotional or very calm, so it does not function as an antonym here.

Common Pitfalls:
Students sometimes confuse “phlegmatic” with “apathetic”, and then assume the antonym must be “interested” or “concerned”. While there is some overlap, exam questions normally expect you to connect “phlegmatic” with “calm and unemotional” and then choose a strongly emotional opposite like “ardent”. To avoid such confusion, try to store temperament words in pairs: phlegmatic–ardent (calm–passionate), indifferent–concerned, and so on. This habit helps you react quickly and accurately when facing antonym questions in competitive exams.

Final Answer:
Correct answer: ardent.