Magniloquent means speaking in a grandiose, pompous manner. Bombastic is an adjective for the language itself, and Sesquipedalian refers specifically to long words, not the speaker's manner.

Ergonomania (ergo=work, mania=excessive desire) means obsessive work addiction. Workaholism is colloquial; Diligence and Industriousness mean normal hard work.

Solipsist believes only their own mind exists. Nihilist denies all meaning, Existentialist focuses on existence and freedom, and Relativist denies absolute truths.

Misogamy (miso=hatred, gamy=marriage) means hatred of marriage. Gamophobia means fear of marriage (phobia=fear), while Misogyny means hatred of women.

Chauvinist shows excessive, aggressive devotion to one's country (from Nicolas Chauvin). Patriot loves country normally; Nationalist emphasizes national identity; Loyalist shows allegiance to ruler/government.

Bite the dust means to be defeated, fail, or die. It's commonly used in competitive contexts.

'Break the ice' means to initiate conversation or ease tension in an awkward situation.

This idiom means working late or studying hard, often for exams or important work.

The idiom means heavy rainfall. Option B correctly uses it in context.

'Hit the books' is a common idiom meaning to study hard, especially used by students.