Choose the sentence with the appropriate Article:

The correct answer is Option (1) → A lion is a dangerous animal.

Articles with a singular countable noun:

• A singular countable noun such as "lion" or "animal" cannot stand alone; it needs an article (a/an/the).
• To speak of a whole class, we can use "a" (A lion ...) or "the" (The lion ...).
• After "is", the noun "animal" again needs "a": "a dangerous animal".
  Example: A cow is a useful animal.

Why the Other Options are Incorrect?

Option 2: Lion is dangerous animal. — Incorrect. Both singular nouns, "lion" and "animal", are left without an article.

Option 3: The lion is dangerous animal. — Incorrect. "The lion" is correct for the class, but "a" is missing before "dangerous animal".

Option 4: Lion is the dangerous animal. — Incorrect.

• "Lion" has no article.
• "The dangerous animal" would mean the one particular dangerous animal, which is not the sense.