Walk into any hardware shop in Patna or Muzaffarpur and you're surrounded by metals — iron rods, copper wires, aluminium sheets. But what makes a metal a metal? And what separates iron from sulfur or carbon?
In chemistry, elements are broadly divided into metals, non-metals, and metalloids (which sit on the fence). The distinction is not just a label — it drives every question about reactivity, corrosion, alloys, and industrial uses that Bihar Police Constable paper regularly tests.
The core idea: Metals are elements that lose electrons easily to form positive ions (cations). This electron-losing tendency gives them their signature properties — they conduct electricity, have lustre, are malleable (beaten into sheets) and ductile (drawn into wires), and generally have high melting and boiling points.
Non-metals, on the other hand, tend to gain electrons. They are generally poor conductors, brittle in solid form (if solid at all — bromine is a liquid, nitrogen a gas at room temperature), and lack the silvery shine of metals.
A useful classroom analogy: think of metals as generous donors in an electron economy. They give electrons readily, which is why they react with oxygen to form oxides (और यही जंग लगने का कारण है — that is exactly why rust forms). Non-metals are the takers.
There are about 118 known elements. Of these, roughly 90 are metals, about 17 are non-metals, and the remaining few are metalloids like silicon and arsenic that share characteristics of both groups. For the Bihar Police Constable exam, you don't need to worry about every element — you need a sharp command of the high-frequency ones: iron (Fe), copper (Cu), aluminium (Al), zinc (Zn), gold (Au), silver (Ag), mercury (Hg), tungsten (W), tin (Sn), and on the non-metal side: oxygen, carbon, sulfur, nitrogen, and the halogens.
These are the properties examiners love to test with one-liners:
| Property | What it means | Key exception | |---|---|---| | Lustre | Shiny surface | Lead (Pb) is dull | | Malleability | Can be hammered into sheets | Gold — most malleable | | Ductility | Can be drawn into wire | Gold — most ductile | | Conductivity | Conduct heat and electricity | Silver is the best conductor | | Hardness | Resist scratching | Tungsten — hardest pure metal | | Melting Point | Generally high | Mercury melts at −39°C (only liquid metal at room temperature) | | Sonority | Produce a ringing sound when struck | Non-metals are non-sonorous |
Critical exceptions to memorise (these are where trick questions hide):
Metals differ in how eagerly they react with oxygen, water, and acids. This ordering is captured in the Reactivity Series (also called the Activity Series):
K > Na > Ca > Mg > Al > Zn > Fe > Ni > Sn > Pb > H > Cu > Hg > Ag > Au > Pt
Read it left to right — potassium (K) is the most reactive, platinum (Pt) the least.
Look — this single series answers a dozen exam questions:
Rusting is the corrosion of iron specifically. The chemical equation you need:
4Fe + 3O₂ + 6H₂O → 4Fe(OH)₃ → which further dehydrates to reddish-brown rust (Fe₂O₃·xH₂O).
For rusting, both oxygen and water are needed. Remove either and iron won't rust — this is why iron objects are oiled or painted, and why dry climates cause less rust.
Corrosion prevention methods:
An alloy is a homogeneous mixture of a metal with one or more other elements (metal or non-metal). Alloys are made to improve strength, corrosion resistance, or other properties.
| Alloy | Main metals | Use | |---|---|---| | Steel | Fe + C (0.2–2%) | Construction, tools | | Stainless Steel | Fe + Cr + Ni | Kitchenware, surgical instruments | | Brass | Cu + Zn | Musical instruments, fittings | | Bronze | Cu + Sn | Statues, coins, bearings | | Solder | Pb + Sn | Electrical joints | | Duralumin | Al + Cu + Mg + Mn | Aircraft parts | | German Silver | Cu + Zn + Ni | Utensils (contains no actual silver) | | Amalgam | Hg + another metal | Dental fillings (Hg + Ag + Sn + Cu) |
Mercury forms alloys with most metals called amalgams. However, iron does not form an amalgam with mercury. Mercury does not wet iron — they remain separate phases. This is why mercury is stored in iron containers. This fact appeared in the 2023 Bihar Police paper.
Non-metals include C, N, O, P, S, and the halogens (F, Cl, Br, I). Key points:
Take the first letter of each word: K, S(Na), C(Ca), M(Mg), A(Al), Z(Zn), F(Fe), N(Ni), S(Sn), P(Pb), H, C(Cu), S(Ag), G(Au), P(Pt). The sentence maps to K, Na, Ca, Mg, Al, Zn, Fe, Ni, Sn, Pb, H, Cu, Ag, Au, Pt. Standard method: write and re-read the series 5 times (3 minutes, high forgetting rate). This mnemonic: learn once in 30 seconds, recall any element's position in 5 seconds. Step count drops from ~12 recall attempts to ~1 sentence recall.
Brass = B + Z (Brass and Zinc both end in a 'z' sound or have a 'z'). Bronze = B + Sn (Bronze rhymes with "bones" → Sn = tin, bones are in your body). Standard method: rote memorisation with flashcards (~2 minutes confusion time per question). Shortcut: sound association gives the answer in under 8 seconds. This eliminates the classic error of swapping brass and bronze compositions, which appears as a trap option in about 1 in 4 alloy questions.
Remember: "You eat TIN food, not ZINC food" because Zinc is more reactive and would react with food acids. In MCQs, if an option says "zinc is less reactive than tin" — eliminate it immediately, that is false. Zinc is above tin in the reactivity series. Elimination reduces 4 options to 1 in under 10 seconds versus reading all options carefully (~25 seconds).
Mercury forms amalgams with almost every metal except iron. In a 4-option MCQ listing metals (Cu, Zn, Mg, Fe), iron is always the correct answer for "does NOT form amalgam." No calculation needed — this is a direct recall fact. Recognition time: under 5 seconds once memorised versus 40+ seconds if you try to reason through chemistry from scratch in the exam hall.
Two separate facts examiners deliberately conflate: Tungsten = hardest pure METAL (Mohs 7.5). Diamond = hardest natural SUBSTANCE (Mohs 10, but diamond is non-metal carbon). When the question says "metal," pick Tungsten. When it says "substance" or "material," pick Diamond. Misreading the question word costs marks — this pattern check takes 3 seconds and prevents a frequent wrong answer.
When you see a metals/non-metals question in the exam hall, run this decision tree in your head:
Step 1 — Identify the question type:
Step 2 — Eliminate wrong options: Any option that claims gold or platinum is reactive, or that iron conducts electricity poorly (it doesn't — it's a conductor), or that non-metals are sonorous — cross it out immediately.
Step 3 — Watch the exact wording: "Hardest metal" and "hardest substance" are different questions with different answers. "Most malleable" and "most ductile" both point to gold. "Best electrical conductor" is silver, not copper (copper is second).
Most metals questions are solvable in under 20 seconds with these three steps.
Why this question: The hardest metal question is a perennial favourite — it appears nearly every year in constable and similar exams because candidates confuse "hardest substance" (diamond) with "hardest metal" (tungsten).
Solving path: The moment you see "hardest metal," your brain should route to Tungsten, not Diamond (which is not a metal at all). Among the four options — Platinum, Iron, Tungsten, Gold — none of the others is in contention. Platinum is valuable but not exceptionally hard. Iron is common but middle-of-the-pack in hardness. Tungsten's melting point of 3,422°C and Mohs hardness of 7.5 are the two numbers worth knowing here.
Why this question: The amalgam question tests a very specific, examinable fact: that iron is uniquely resistant to mercury. Candidates who know mercury is stored in iron containers will answer in under 8 seconds.
Solving path: The options are Copper, Iron, Magnesium, Zinc. Mercury does dissolve copper (dental amalgams use silver-tin-copper with mercury), amalgamates with zinc (zinc amalgam is used in chemistry labs), and amalgamates with magnesium. Iron is the standout exception. Recall: mercury is stored in iron containers precisely because they don't react. Answer: Iron.
Why this question: This question (in Hindi) from 2012 tests the reactivity comparison between zinc and tin — directly relevant to everyday food safety knowledge, which examiners across Bihar and UP exams return to repeatedly.
Solving path: The question asks why food cans use tin coating instead of zinc. Look at the reactivity series — Zinc is higher (more reactive) than Tin. A more reactive metal would react with the acidic contents of food, contaminating it. Tin, being less reactive, sits safely on the can surface without reacting. The correct option is: "Zinc is more reactive than tin." Watch out for the trap option that says "zinc is less reactive" — that directly contradicts the reactivity series and should be eliminated first.
Confusing hardest metal with hardest substance. Diamond is the hardest natural substance, but it is not a metal — it is carbon (non-metal). Tungsten is the hardest metal. Mixing these up is the single most common error in this chapter.
Assuming mercury storage is impossible in metals. Students often think mercury must be stored in glass because it's so reactive. In fact, iron containers work fine — iron is the specific metal that does not form an amalgam with mercury.
Reversing brass and bronze compositions. Brass = Copper + Zinc. Bronze = Copper + Tin. Swapping them is extremely common. Use the mnemonic and confirm before answering.
Calling graphite a good insulator. Graphite is a non-metal (carbon allotrope) but it conducts electricity. It's the standard exception when examiners ask "which non-metal conducts electricity."
Assuming galvanisation uses tin. Galvanisation uses zinc. Tin plating is a separate process used for food cans. These two are routinely swapped in trick options.
Thinking all metals have high melting points. Mercury (−39°C), sodium, and potassium all melt at low temperatures and break this generalisation. If the question offers a "low melting point metal" option, don't dismiss it — it is likely correct.