Why this chapter matters for UPSC: Grouping things by their properties is how chemistry begins: metals and non-metals, soluble and insoluble, transparent and opaque. Prelims general science tests the properties and their exceptions (mercury is a liquid metal, graphite a conducting non-metal, diamond the hardest natural substance), and GS3 now asks about the minerals India needs for batteries and electronics. In NCERT's rationalised 2023-24 edition this is Chapter 2, "Sorting Materials into Groups", with the text unchanged.

🧠 First Principles — Read This First

There is a vast variety of objects around us: a chair, a bullock cart, a cycle, utensils, books, toys, water, stones. NCERT shows that we can group them in many ways: by shape (round things: a ball, a marble, an apple, a gharha), by use (things we eat), or by the material they are made of (plastic buckets, lunch boxes, pipes).

Three observations follow:

  1. An object may be made of one material or many; and one material may be used for many objects.
  2. We choose a material for an object according to its properties and the purpose of the object. A tumbler made of cloth would be silly; so would a paper cooking pot.
  3. Materials can therefore be grouped by their properties: appearance (lustre), hardness, solubility, whether they float or sink, and transparency.

Grouping is useful: a grocer keeps biscuits, soaps and grains in separate places, and grouping materials helps us study their properties and see patterns in them.

PART 1 — Quick Reference

Properties of Materials (NCERT)

PropertyWhat it meansNCERT examples
LustreShine, best seen on a freshly cut or sand-papered surfaceIron, copper, aluminium, gold (metals); they may look dull because of air and moisture
HardnessHard materials are difficult to compress or scratch; soft ones are easyIron is hard; cotton and sponge are soft
Soluble in waterDisappears completely on stirringSugar, salt
Insoluble in waterDoes not mix even after long stirringChalk powder, sand, sawdust
LiquidsSome mix well with water; others form a separate layerVinegar and lemon juice mix well; mustard oil, coconut oil and kerosene do not
GasesSome dissolve in waterDissolved oxygen is vital for plants and animals living in water
Floats or sinksInsoluble materials either rise to the surface or settleDried leaves float; a stone sinks
TransparentThings can be seen through itGlass, water, air, some plastics
TranslucentThings can be seen, but not clearlyOiled paper; the oily patch from the fat test
OpaqueThings cannot be seen through itWood, cardboard, metals

Objects and Materials (NCERT Tables 4.1 and 4.2)

MaterialObjects made from it
WoodChair, table, plough, bullock cart and its wheels
PaperBooks, notebooks, newspaper, toys, calendars
PlasticsBuckets, lunch boxes, toys, water containers, pipes
Steel, glass, plasticsA plate (thali) can be made of any of these

PART 2 — Concepts & Narrative

Appearance and Hardness

NCERT's teacher cuts paper, cardboard, wood, copper wire, aluminium sheet and chalk and asks which freshly cut surfaces shine. Materials with such lustre are usually metals: iron, copper, aluminium, gold. Metals often look dull because air and moisture act on them, so the shine shows best on a fresh cut; look at freshly cut rods in an ironsmith's workshop. NCERT Class X names this dulling corrosion: the black coating on silver and the green coating on copper, as well as rust on iron.

Press materials with your hands or scratch them with a metal key: some compress or scratch easily (soft: cotton, sponge), others do not (hard: iron). Materials can also be rough or smooth.

Solubility, Floating and Sinking

Stir a spoonful each of sugar, salt, chalk powder, sand and sawdust into glasses of water: sugar and salt dissolve (soluble); the rest do not (insoluble). Water plays an important role in our body precisely because it dissolves a large number of substances. Among liquids, vinegar and lemon juice mix well with water; mustard oil, coconut oil and kerosene form a separate layer. Some gases dissolve too: oxygen dissolved in water keeps aquatic plants and animals alive (Paheli's question). Insoluble materials either float (dried leaves) or sink (a stone, drops of honey).

Transparent, Translucent, Opaque

In hide-and-seek nobody hides behind a glass window. Materials we can see through are transparent (glass, water, air, some plastics), which is why shopkeepers keep sweets and biscuits in glass or plastic jars. Materials we cannot see through are opaque (wood, cardboard, metals). NCERT's oiled-paper activity shows a third group: a sheet of paper with a few drops of oil lets the bulb be seen, but not clearly: it is translucent. Paheli's question: is the palm of your hand opaque, transparent or translucent when you shine a torch through it in the dark?

Key Term

Metals and non-metals (NCERT Classes VIII and X): the properties in this chapter become the first big grouping in chemistry.

PropertyMetalsNon-metals
LustreLustrousGenerally dull
MalleabilityCan be beaten into sheetsBrittle; break into pieces (coal, pencil lead)
DuctilityCan be drawn into wires (aluminium, copper)Not ductile
SonoritySonorous: produce a ringing sound when struckNot sonorous
ConductionGood conductors of heat and electricityGenerally poor conductors
OxidesGenerally basic (magnesium oxide turns red litmus blue)Generally acidic

Exceptions NCERT Class X lists:

  • All metals are solids at room temperature except mercury. Gallium and caesium melt so easily that they melt on your palm.
  • Iodine is a non-metal but lustrous.
  • Carbon exists as allotropes: diamond is the hardest natural substance known; graphite conducts electricity.
  • Alkali metals (lithium, sodium, potassium) are so soft they can be cut with a knife. Sodium reacts so vigorously with air and water that it is stored in kerosene (NCERT VIII).

How Metals and Non-metals Behave (NCERT Class VIII)

Chemical behaviour separates the two groups more clearly than appearance does:

  • With acids: metals generally react and give hydrogen gas, which burns with a "pop" sound near a lit matchstick; non-metals generally do not react. Copper does not react with dilute hydrochloric acid even on heating, but reacts with sulphuric acid.
  • Displacement: a more reactive metal displaces a less reactive one from its compound, never the reverse. Zinc displaces copper and iron; iron displaces copper. So the order of reactivity among the three is zinc > iron > copper.
  • Uses: metals make machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, cooking utensils and water boilers. Non-metals are just as essential, and NCERT asks students to name them: the non-metal all living beings inhale (oxygen), non-metals in fertilisers, a non-metal used in water purification, one in the purple antiseptic solution applied on wounds, and non-metals in crackers.

Alloys: Changing a Metal's Properties (NCERT Class X)

Explainer

An alloy is a homogeneous mixture of two or more metals, or of a metal and a non-metal, made by melting the main metal and dissolving the others in it. Pure iron is soft and stretches when hot; with a little carbon (about 0.05%) it becomes hard and strong.

AlloyMade of (NCERT X)Note
SteelIron + a little carbonHard and strong
Stainless steelIron + nickel + chromiumHard and does not rust
BrassCopper + zincNot a good conductor
BronzeCopper + tinNot a good conductor
SolderLead + tinLow melting point; used to weld electrical wires together
AmalgamAny alloy with mercury
22-carat gold22 parts gold + 2 parts copper or silverPure (24-carat) gold is too soft for jewellery

Rule to remember: an alloy's electrical conductivity and melting point are lower than those of the pure metals in it. That is why copper, not brass or bronze, is used for electric circuits.

Preventing corrosion: painting, oiling, greasing, galvanising (a zinc coat), chrome plating, anodising, or making alloys.

Materials That Matter Today: Critical Minerals

UPSC Connect

Critical minerals are the materials of batteries, solar panels, electronics and defence equipment. In 2023 the Ministry of Mines released a list of 30 critical minerals for India, including lithium, cobalt, nickel, graphite, copper, the rare earth elements (REE), the platinum group elements (PGE), gallium, germanium, silicon, titanium, tungsten, vanadium and zirconium.

  • National Critical Mineral Mission: approved by the Union Cabinet on 29 January 2025 with ₹16,300 crore of government spending and an expected ₹18,000 crore from public-sector undertakings and others (a total of ₹34,300 crore over seven years). It covers the whole value chain: exploration, mining, beneficiation, processing and recovery from end-of-life products. It also provides for mineral processing parks, a national stockpile, recycling, overseas acquisition of mineral assets, and a Centre of Excellence on Critical Minerals.
  • Recycling incentive scheme: approved on 3 September 2025: ₹1,500 crore for FY 2025-26 to 2030-31, to build at least 270 kilotonnes of annual recycling capacity yielding about 40 kilotonnes of critical minerals a year from e-waste, lithium-ion battery scrap and other scrap such as catalytic converters.

PART 3 — UPSC Integration

The chapter turns a common-sense habit, sorting things, into a scientific method: group by a property, then look for patterns. That method leads straight to the classification of elements into metals and non-metals, to the exceptions examiners love, and to alloys designed to change a metal's behaviour. It also explains everyday choices: glass jars in shops (transparency), copper wire (conductivity, ductility), galvanised pipes (corrosion), steel and aluminium utensils (strength, conduction). In current affairs, the same thinking explains why lithium, graphite and rare earths are "critical": their properties make them hard to replace in batteries, magnets and electronics. Answers should state the property, the material and the use together.

Exam Strategy

Prelims traps:

  • Lustre shows best on a freshly cut surface; metals dull because of air and moisture (corrosion).
  • Translucent = seen through but not clearly (oiled paper); not the same as transparent.
  • Oil and water do not mix; vinegar and lemon juice do.
  • Mercury is the only metal liquid at room temperature; gallium and caesium melt on the palm.
  • Iodine: a lustrous non-metal. Graphite: a non-metal that conducts. Diamond: hardest natural substance.
  • Sodium is stored in kerosene.
  • Alloys conduct less and melt lower than pure metals; solder (lead + tin) has a low melting point.
  • 22-carat gold = 22 parts gold + 2 parts copper or silver; an alloy with mercury is an amalgam.
  • Critical minerals: 30 on the 2023 list; NCMM approved 29-Jan-2025.

Mains angle: Explain why some minerals are "critical" for India's energy transition and what the National Critical Mineral Mission does about it.

Practice Questions

Practice (UPSC-pattern, not past papers).

Prelims:

  1. A sheet of paper with a few drops of oil on it lets you see a lighted bulb, but not clearly. The oiled paper is:
    (a) Transparent
    (b) Translucent
    (c) Opaque
    (d) Lustrous

  2. Which one of the following metals is a liquid at room temperature?
    (a) Mercury
    (b) Gallium
    (c) Caesium
    (d) Sodium

  3. Consider the following statements:

    1. Iodine is a non-metal but is lustrous.
    2. Graphite is a non-metal that conducts electricity.
    3. Diamond is a metal and the hardest natural substance known.
      Which of the statements given above are correct?
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

  4. Solder, used to join electrical wires, is an alloy of:
    (a) Copper and zinc
    (b) Copper and tin
    (c) Lead and tin
    (d) Iron and chromium

  5. Which of the following substances will NOT dissolve in water?
    (a) Sugar
    (b) Salt
    (c) Sand
    (d) Lemon juice

  6. Copper rather than brass is used for electric wiring mainly because:
    (a) Brass is too soft
    (b) An alloy conducts electricity less well than the pure metal
    (c) Brass is not ductile
    (d) Copper does not corrode

  7. With reference to the National Critical Mineral Mission, consider the following statements:

    1. It was approved by the Union Cabinet in January 2025.
    2. It covers exploration, mining, processing and recovery from end-of-life products.
    3. It is funded entirely by the private sector.
      Which of the statements given above are correct?
      (a) 1 and 2 only
      (b) 2 and 3 only
      (c) 1 and 3 only
      (d) 1, 2 and 3

Mains (UPSC-pattern):

  1. "The properties of a material decide its use." Illustrate with examples of metals, non-metals and alloys. (150 words)
  2. Why are critical minerals important for India's energy transition, and how does the National Critical Mineral Mission propose to secure them? (150 words)

📦 Revision Capsule

Revision Capsule

Hard Facts

  • Objects can be grouped by shape, use or material; choose materials by properties and purpose
  • Properties: lustre, hardness, solubility, float or sink, transparency
  • Soluble: sugar, salt; insoluble: chalk, sand, sawdust; oil does not mix with water; dissolved oxygen sustains aquatic life
  • Transparent (glass, water, air), translucent (oiled paper), opaque (wood, cardboard, metals)
  • Metals: lustrous, malleable, ductile, sonorous, conduct, basic oxides; exceptions: mercury, gallium, caesium, soft alkali metals
  • Non-metal exceptions: iodine (lustrous), graphite (conducts), diamond (hardest)
  • Alloys: brass (Cu + Zn), bronze (Cu + Sn), solder (Pb + Sn), stainless steel (Fe + Ni + Cr), amalgam (with Hg); 22-carat gold
  • NCMM: approved 29-Jan-2025; ₹16,300 cr + ₹18,000 cr; 30 critical minerals (2023 list)

Core Concepts

  • Grouping by properties reveals patterns
  • Alloys change a metal's properties: harder, lower conductivity, lower melting point
  • Corrosion explains why metals lose their shine

Confused Pairs

  • Transparent vs translucent vs opaque
  • Soluble (dissolves) vs mixes well (liquids) vs floats (insoluble, lighter)
  • Brass (copper + zinc) vs bronze (copper + tin)
  • Diamond (hardest, does not conduct) vs graphite (conducts); both carbon

PYQ Pattern

  • No question in BharatNotes' PYQ bank tests this chapter directly. Expect Prelims general science on properties of metals and non-metals, their exceptions, alloys, and critical minerals.

Sources

Sources