Chemistry Questions for SSC CGL

Periodic Table Trends & Element Properties

SSC loves asking about trends as you move across a period or down a group. Atomic radius decreases left-to-right (more protons pull electrons closer). Ionization energy increases left-to-right (harder to remove electrons). Electronegativity increases left-to-right. Down a group, atomic radius increases (more shells), ionization energy decreases (electrons farther from nucleus). Metals are on the left, non-metals on the right. Halogens (Group 17) are most reactive non-metals; noble gases (Group 18) are inert. Common PYQ: Which element has highest electronegativity? (Fluorine, always.) Which has lowest? (Francium.) Which is most reactive metal? (Francium, but sodium/potassium more commonly asked.)

• Atomic radius: decreases across period, increases down group
• Ionization energy: increases across period, decreases down group
• Electronegativity: F > O > N > Cl (fluorine always highest)
• Metals lose electrons (reducing agents); non-metals gain electrons (oxidizing agents)
• Transition metals (d-block) show variable oxidation states — common in redox questions
• Lanthanides & actinides rarely tested in Tier-1, skip for speed

Acids, Bases & pH

Acids donate H+ ions (protons); bases accept H+ ions or donate OH- ions. pH = -log[H+]. pH < 7 is acidic, pH = 7 is neutral, pH > 7 is basic. Strong acids (HCl, HNO3, H2SO4) completely ionize; weak acids (acetic acid, carbonic acid) partially ionize. Strong bases (NaOH, KOH) completely ionize; weak bases (ammonia) partially ionize. Neutralization: acid + base → salt + water. Common PYQ: What is the pH of pure water? (7.) Which is stronger acid, HCl or acetic acid? (HCl.) What happens when you add acid to water? (Heat is released — exothermic.) SSC often asks about everyday acids: lemon juice (citric acid), vinegar (acetic acid), stomach acid (HCl).

• Strong acids: HCl, HNO3, H2SO4, HBr, HI, HClO4
• Strong bases: NaOH, KOH, Ca(OH)2, Ba(OH)2
• pH scale: 0-14; below 7 acidic, above 7 basic
• Neutralization produces salt (not always NaCl — any ionic compound from acid + base)
• Indicators: litmus (red in acid, blue in base), methyl orange, phenolphthalein
• Buffer solutions resist pH change — common in Tier-2

Oxidation & Reduction (Redox)

Oxidation is loss of electrons (or gain of oxygen, or loss of hydrogen). Reduction is gain of electrons (or loss of oxygen, or gain of hydrogen). Oxidizing agent causes oxidation (itself gets reduced); reducing agent causes reduction (itself gets oxidized). Oxidation number rules: element in pure form = 0; monatomic ion = charge; oxygen usually -2 (except in peroxides where it's -1); hydrogen usually +1 (except in metal hydrides where it's -1). SSC Tier-1 asks: identify oxidation states, balance simple redox equations, name the oxidizing/reducing agent. Tier-2 goes deeper into half-reactions and balancing in acidic/basic media.

• Oxidation number increases = oxidation (loses electrons)
• Oxidation number decreases = reduction (gains electrons)
• Oxidizing agent: the substance that gets reduced (gains electrons)
• Reducing agent: the substance that gets oxidized (loses electrons)
• In redox, electrons lost = electrons gained
• Common redox pairs: Fe2+/Fe3+, Mn2+/MnO4-, S/SO42-, C/CO2

Metals, Non-metals & Metalloids

Metals: shiny, malleable, ductile, good conductors of heat & electricity, lose electrons to form cations. Non-metals: dull, brittle, poor conductors, gain electrons to form anions. Metalloids (B, Si, Ge, As, Sb, Te): properties between metals and non-metals; semiconductors. Reactivity series of metals (most to least reactive): K > Na > Ca > Mg > Al > Zn > Fe > Pb > H > Cu > Hg > Ag > Au. A more reactive metal displaces a less reactive metal from its salt solution. Corrosion (rusting of iron): Fe + O2 + H2O → Fe2O3·xH2O (requires oxygen and water). Alloys: mixtures of metals (brass = Cu + Zn, steel = Fe + C). SSC asks: which metal is most reactive? (Potassium.) Which is least reactive? (Gold.) What causes rusting? (Oxygen + water + iron.)

• Reactivity series: K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au
• More reactive metal displaces less reactive from salt solution
• Rusting requires three: iron + oxygen + water (prevent by painting, oiling, galvanizing)
• Alloys are stronger than pure metals — used in construction, jewelry, tools
• Non-metals form covalent bonds; metals form ionic bonds
• Amphoteric metals (Al, Zn) react with both acids and strong bases

Chemical Reactions & Equations

Types of reactions: combination (A + B → AB), decomposition (AB → A + B), displacement (A + BC → AC + B), double displacement (AB + CD → AD + CB), combustion (fuel + O2 → CO2 + H2O + heat), neutralization (acid + base → salt + water). Balancing equations: count atoms on both sides; use coefficients (not subscripts). Exothermic reactions release heat (combustion, neutralization, rusting); endothermic reactions absorb heat (melting, evaporation, photosynthesis). SSC Tier-1 asks: identify reaction type, balance simple equations, predict products. Tier-2 asks: state symbols (s, l, g, aq), energy changes, limiting reagent.

• Combination: simple substances → compound
• Decomposition: compound → simpler substances (often needs heat or electricity)
• Displacement: one element replaces another in a compound
• Double displacement: ions swap partners; often produces precipitate or gas
• Combustion: always produces CO2 + H2O (+ heat); requires oxygen
• Exothermic: releases energy (ΔH negative); endothermic: absorbs energy (ΔH positive)

Water Hardness & Everyday Chemistry

Hard water contains dissolved Ca2+ and Mg2+ ions. Temporary hardness caused by Ca(HCO3)2 and Mg(HCO3)2 — removed by boiling (heat decomposes bicarbonates). Permanent hardness caused by CaSO4 and MgSO4 — removed by adding Na2CO3 (precipitates Ca2+ and Mg2+) or using ion-exchange resins. Soft water lathers easily with soap; hard water forms scum. SSC loves this topic: What causes hard water? (Ca2+ and Mg2+ ions.) How to remove temporary hardness? (Boiling.) How to remove permanent hardness? (Add Na2CO3 or use ion-exchanger.) Soap chemistry: long-chain fatty acids + NaOH → soap (sodium salt of fatty acid). Detergents are synthetic soaps, work in hard water.

• Hard water: contains Ca2+ and Mg2+ ions
• Temporary hardness: Ca(HCO3)2, Mg(HCO3)2 — removed by boiling
• Permanent hardness: CaSO4, MgSO4 — removed by Na2CO3 or ion-exchanger
• Soap: sodium salt of long-chain fatty acid; doesn't work well in hard water
• Detergents: synthetic soaps; work in hard and soft water
• Scum: insoluble calcium/magnesium salts of fatty acids formed in hard water

Atomic Structure & Bonding Basics

Atom: nucleus (protons + neutrons) + electrons in shells. Protons = atomic number (defines element). Protons + neutrons = mass number. Electrons = protons (in neutral atom). Isotopes: same atomic number, different mass number (e.g., C-12 and C-14). Ionic bond: transfer of electrons (metal to non-metal); forms cations and anions. Covalent bond: sharing of electrons (between non-metals). Metallic bond: sea of delocalized electrons (in metals). Electronegativity difference > 1.7 typically indicates ionic bond; < 0.4 indicates non-polar covalent; 0.4-1.7 indicates polar covalent. SSC Tier-1 asks: identify bond type, calculate atomic/mass number. Tier-2 asks: VSEPR theory, hybridization (skip for Tier-1).

• Atomic number = number of protons (defines element)
• Mass number = protons + neutrons
• Isotopes: same atomic number, different mass number
• Ionic bond: electron transfer (high electronegativity difference)
• Covalent bond: electron sharing (low electronegativity difference)
• Metallic bond: delocalized electron sea in metals

• Confusing oxidation with oxidation number — oxidation is a process (loss of electrons), oxidation number is a label assigned by rules. In redox, track oxidation numbers, not just electron count.
• Thinking all salts are NaCl — salts are ANY ionic compound from acid + base. CuSO4, NH4Cl, KNO3 are all salts. This trips up neutralization questions.
• Memorizing reactivity series wrong — K is most reactive metal, not Na. Francium is theoretically most reactive but K is the practical answer in SSC. Gold is least reactive, not silver.
• Assuming hard water is caused only by Ca2+ — Mg2+ is equally important. Both cause hardness; both are removed the same way.
• Balancing equations by changing subscripts — NEVER change subscripts (that changes the compound). Only change coefficients (the numbers in front).
• Forgetting that rusting needs THREE things — iron alone doesn't rust; oxygen alone doesn't cause rust; water alone doesn't cause rust. All three together cause rust. This is a classic Tier-2 trap.

• OILRIG = Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons) — use this to never confuse oxidation and reduction again.
• Reactivity series mnemonic: 'Please Keep Calling My Animal A Zebra In Pasture, Horses Cry Mournfully' = K, Ca, Na, Mg, Al, Zn, I (iron), P (Pb), H, Cu, Hg, Ag. (Imperfect but helps.)
• pH < 7 Acidic, pH = 7 Neutral, pH > 7 Basic — think 'A' for Acidic comes before 'B' for Basic in alphabet, and 'A' is less than 'B' numerically.
• Rusting = Iron + Oxygen + Water — remember 'IOW' (I Owe Water) to recall all three ingredients.
• Hard water has Ca2+ and Mg2+ — think 'CaMg' (like a brand name) to remember both ions.

• Tier-1 (90 seconds per question): Expect 5-8 chemistry questions. Most are definition-based or require one-step reasoning. Reactivity series, pH scale, hard water, and redox identification dominate. Skip lengthy calculations; if a question needs more than 45 seconds, you've misunderstood it.
• Tier-2 (2-3 minutes per question): Expect 10-15 questions. Deeper conceptual traps appear here — e.g., 'Which metal displaces copper from CuSO4?' (Answer: Fe, Zn, or any more reactive metal, but NOT Ag or Au.) Balancing equations and oxidation state calculations are common.
• Recent PYQ patterns (2022-2024): Hard water questions appear almost every year (Tier-1 and Tier-2). Reactivity series displacement questions are frequent. Redox identification (oxidizing agent vs. reducing agent) appears 1-2 times per paper. Expect 1-2 questions on everyday chemistry (rusting, soap, combustion).
• Avoid memorizing complex mechanisms or derivations — SSC tests recognition and application, not derivation. Know WHAT happens, not WHY in detail (unless Tier-2 explicitly asks).
• Use elimination aggressively in Tier-1. If a question asks 'Which is the strongest acid?', eliminate noble gases, metals, and non-reactive elements first. Chemistry questions often have obvious wrong answers.