Step 1: Understanding the Concept:
This question evaluates the correct usage of prepositions, idiomatic phrases, and lexical collocations in English sentences.
Step 2: Detailed Explanation:
1. Analysis of (1): The phrase "in once" is incorrect. The correct idiomatic expression to mean "immediately" or "at the first attempt" is "at once".
2. Analysis of (2): This sentence is grammatically sound. "Anxious" is an adjective correctly used to describe the nature of the "hour" (time spent in worry), and the structure is clear.
3. Analysis of (3): "Inculcate" means to instill an idea or habit through persistent instruction. It is generally used for positive traits (e.g., inculcating values). One does not typically "inculcate" a negative habit like "finding fault." A better verb would be "develop" or "acquire".
4. Analysis of (4): This is a famous proverb, but it is missing a preposition. The correct version is "A drowning man catches at a straw". Without "at", the sentence is idiomatically incomplete.
Step 3: Final Answer:
Sentence (2) is the only one that adheres to standard grammatical and idiomatic rules.