Choose the sentence with the appropriate Article:

The correct answer is Option (2) → The rich should help the poor.

"The" + adjective:

• The + adjective is used for a whole class of people: the rich (rich people), the poor (poor people), the old.
• Such a phrase takes a plural verb and needs "the".
• This sentence: "The rich" and "the poor" both have the article, so it is correct.
  Example: The young should respect the old.

Why the Other Options are Incorrect?

Option 1: Sun rises in east. — Incorrect. Things that are one of a kind and the directions take "the": "The sun rises in the east."

Option 3: He is most interesting man. — Incorrect. A superlative needs "the": "He is the most interesting man" (or "a most interesting man", meaning a very interesting man).

Option 4: They are in the trouble. — Incorrect. The fixed phrase is "in trouble", without an article.