Chemistry Basics Questions for RRB GROUP D

Matter and Its States

Matter is anything that has mass and occupies space. It exists in three common states: solid, liquid, and gas. In solids, particles are tightly packed. In liquids, particles flow but stay close. In gases, particles move freely. A fourth state called plasma exists in stars and lightning. Changes between states are called physical changes — the substance remains the same chemically.

• Solid: fixed shape and volume. Example: ice
• Liquid: fixed volume, no fixed shape. Example: water
• Gas: no fixed shape or volume. Example: steam
• Melting point of ice = 0 degrees Celsius, Boiling point of water = 100 degrees Celsius
• Sublimation: solid directly becomes gas. Example: camphor, dry ice (CO2)
• Plasma: found in sun, neon signs, lightning

Elements, Compounds, and Mixtures

An element is a pure substance made of only one type of atom. It cannot be broken down further by chemical means. Example: oxygen (O), iron (Fe), gold (Au). A compound is formed when two or more elements chemically combine in a fixed ratio. Example: water (H2O), salt (NaCl). A mixture is a combination of two or more substances that are NOT chemically combined. Mixtures can be separated by physical methods like filtration, distillation, or evaporation.

• Total elements discovered: 118. Naturally occurring: 92
• Water (H2O) — compound. Air — mixture
• Homogeneous mixture: uniform throughout. Example: saltwater
• Heterogeneous mixture: not uniform. Example: sand and water
• Compounds have fixed composition; mixtures do not
• Alloys are mixtures — brass = copper + zinc, bronze = copper + tin, steel = iron + carbon

Acids, Bases, and Salts

Acids are substances that release hydrogen ions (H+) in water. They taste sour and turn blue litmus red. Bases release hydroxide ions (OH-) and turn red litmus blue. They taste bitter and feel soapy. When an acid and base react, they form salt and water — this is called neutralization. pH scale measures how acidic or basic a solution is. pH 7 is neutral, below 7 is acidic, above 7 is basic.

• Common acids: HCl (hydrochloric), H2SO4 (sulphuric), HNO3 (nitric), CH3COOH (acetic/vinegar)
• Common bases: NaOH (caustic soda), Ca(OH)2 (lime water), Mg(OH)2 (milk of magnesia)
• Acid + Base = Salt + Water (neutralization)
• pH of blood = 7.4 (slightly basic), pH of lemon = 2 (acidic), pH of milk = 6.5
• Indicators: litmus, phenolphthalein, methyl orange
• Baking soda = NaHCO3 (basic), Washing soda = Na2CO3

Chemical Reactions and Types

A chemical reaction is a process where substances (reactants) change into new substances (products) with different properties. Energy is either released or absorbed during a reaction. Key types of reactions asked in exams are: combination, decomposition, displacement, and redox reactions.

• Combination: A + B = AB. Example: C + O2 = CO2
• Decomposition: AB = A + B. Example: 2H2O = 2H2 + O2 (electrolysis of water)
• Displacement: more reactive metal pushes out less reactive one. Example: Zn + CuSO4 = ZnSO4 + Cu
• Oxidation: gain of oxygen or loss of hydrogen. Reduction: loss of oxygen or gain of hydrogen
• Exothermic reaction: releases heat. Example: burning of coal, respiration
• Endothermic reaction: absorbs heat. Example: photosynthesis, cooking food

Periodic Table Basics

The Periodic Table arranges all 118 elements by increasing atomic number. It has 18 vertical columns called groups and 7 horizontal rows called periods. Elements in the same group have similar chemical properties. The table was created by Dmitri Mendeleev in 1869 (arranged by atomic mass). The modern periodic table is based on atomic number.

• Groups (columns): 1 to 18. Periods (rows): 1 to 7
• Group 1 = Alkali metals (Li, Na, K) — very reactive
• Group 17 = Halogens (F, Cl, Br, I) — highly reactive non-metals
• Group 18 = Noble gases (He, Ne, Ar) — inert, do not react
• Lightest element: Hydrogen (H). Heaviest natural element: Uranium (U)
• Most abundant element in Earth's crust: Oxygen. In universe: Hydrogen

Important Chemical Compounds in Daily Life

RRB Group D frequently asks about common chemicals and their names. Knowing the chemical name, formula, and everyday use of about 10-12 compounds will help you directly answer 1-2 questions without any calculation.

• Common salt = NaCl (sodium chloride)
• Baking soda = NaHCO3 (sodium bicarbonate) — used in cooking
• Plaster of Paris = CaSO4 half H2O — used in bandages and moulds
• Bleaching powder = Ca(OCl)Cl — used as disinfectant
• Rust = Fe2O3 nH2O (iron oxide) — forms when iron reacts with oxygen and moisture
• LPG main component = Butane (C4H10). CNG main component = Methane (CH4)

• Confusing baking soda (NaHCO3) with washing soda (Na2CO3) — exam often asks which is which
• Thinking alloys are compounds — alloys like brass and steel are MIXTURES, not compounds
• Mixing up oxidation and reduction — remember OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons)
• Saying Mendeleev arranged by atomic number — he used atomic MASS; atomic number came with Moseley later
• Confusing exothermic and endothermic — students often mark photosynthesis as exothermic, but it absorbs sunlight so it is endothermic

• ACID turns blue litmus RED — A before B, Acid before Base in alphabet like blue before red in effects
• OIL RIG — Oxidation Is Loss of electrons, Reduction Is Gain of electrons
• Alkali metals group 1 — think ONE reactive family all standing in a LINE (period 1 to 7)
• For common salts remember: NaCl = kitchen, NaHCO3 = kitchen baking, Na2CO3 = laundry washing — Na is everywhere in your house
• Noble gases = party guests who talk to NO ONE — zero reactivity, Group 18

• RRB Group D asks 1 direct question on pH — just memorize: lemon is 2, blood is 7.4, neutral is 7. That is enough.
• Chemical name of common substances is a guaranteed question — prepare a list of 10 compounds with formulas and uses. No theory needed.
• Questions on types of chemical reactions are direct — you will see a reaction written and asked to identify its type. Practice spotting combination vs decomposition vs displacement.
• Periodic table questions in Group D are basic — most asked facts are lightest element, most abundant element, noble gases, and who made the table.
• Avoid spending more than 30-40 seconds per chemistry question. These are recall-based, not calculation-based. If you know the fact, answer in 10 seconds and move on.