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Pyrrole is a five-membered aromatic heterocycle containing 6 π-electrons, satisfying Hückel's (4n + 2) rule. Tetrahydrofuran, pyrrolidine, and piperidine are saturated heterocyclic compounds and are therefore non-aromatic.

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Etoposide and Teniposide inhibit Topoisomerase II, whereas Irinotecan inhibits Topoisomerase I. Topotecan is also a Topoisomerase I inhibitor, not a Topoisomerase III inhibitor. Therefore, option D is the incorrect pair.

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Methotrexate resistance commonly occurs due to reduced cellular uptake through impaired reduced folate carrier (RFC) transport and increased expression or gene amplification of dihydrofolate reductase (DHFR). Increased polyglutamate formation generally enhances methotrexate activity rather than resistance.

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Most intravenous anaesthetic agents such as propofol, thiopental, etomidate, and midazolam potentiate GABAA receptor-mediated chloride influx, producing neuronal hyperpolarization and CNS depression.

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Organophosphate compounds irreversibly inhibit acetylcholinesterase, resulting in excessive accumulation of acetylcholine at cholinergic synapses and producing muscarinic manifestations such as salivation, lacrimation, urination, defecation, gastrointestinal cramps, and emesis (SLUDGE syndrome).