Chemistry — Elements, Compounds, Chemical Reactions
Introduction
This chapter is your comprehensive guide to the core of chemistry as tested in the Bihar Public Service Commission (BPSC) examinations. The subtopic "Chemistry – elements, compounds, chemical reactions" is one of the most frequently recurring areas in the Science section, with 61 questions appearing in the available PYQ bank covering exams from 2018 to 2025. This density makes it a high-yield area for any serious aspirant. The questions span a broad spectrum: from fundamental concepts of atomic structure and bonding to applied topics like alloys, industrial compounds, and everyday chemistry (fire extinguishers, fertilisers, polymers).
The BPSC syllabus explicitly requires knowledge of elements, compounds, and chemical reactions – but the PYQs reveal a deeper expectation. You must be comfortable with:
- Atomic and nuclear structure (protons, neutrons, electrons, mass number, isotopes).
- Chemical bonding (sigma/pi bonds, bond order, molecular geometry).
- Acids, bases, and pH (scale, H⁺ concentration, neutralisation).
- Metals and metallurgy (alloys, ores, extraction processes, corrosion).
- Important compounds and materials (quicklime, nitrous oxide, greenhouse gases, polymers, medicines).
- Reaction types and rates (exothermic/endothermic, catalysis, displacement reactions).
The level of difficulty is generally moderate – most questions test direct recall of facts or simple applications (e.g., calculating neutrons from mass number and atomic number). However, a few questions require analytical thinking (e.g., predicting weight changes during rusting, understanding pH logarithm). The examiners often repeat concepts across years – for example, the composition of brass appears in 2021, and German silver appears in 2022; quicklime is asked in both 2021 and 2022; rusting weight appears in 2021 and 2022. This indicates that mastery of the PYQs gives you a strong advantage, but you must also be prepared for lateral extensions (e.g., new alloys, new polymers).
In this chapter, you will not only learn the answers to every PYQ but also the why behind them. We will build concepts from first principles, define every term, use tables for comparisons, and provide memory aids you can use the night before the exam. By the end, you should be able to solve any current or future question on elements, compounds, and chemical reactions with confidence.