12th Chemistry Important 1 Mark Questions Chapter Wise (Samacheer Kalvi)

By Ravi Kumar · 9 Jul 2026 · 4 min read

Chemistry has the largest number of one-mark questions of the three science subjects, and the most predictable ones. The concepts recur, the phrasing recurs, and nearly all of it comes from the textbook evaluation sections.

Here is what gets asked, unit by unit.

Unit 1: Metallurgy

Which ore belongs to which metal
Concentration methods and which ore each suits
Roasting versus calcination
Ellingham diagram interpretation
Refining methods: van Arkel, Mond process, zone refining and what each is used for

The refining-method-to-metal pairing is asked almost every year. Learn it as a table.

Units 2 and 3: p-Block Elements

Diborane structure and banana bonds
Why boric acid behaves as an acid, and its structure
Catenation and which elements show it
Allotropes of carbon and their properties
Hydrolysis products of phosphorus halides
Basicity of oxyacids of phosphorus
Interhalogen compounds and noble gas compounds with their shapes

Basicity questions on phosphorus oxyacids are a reliable trap. Basicity counts the hydrogens directly bonded to oxygen, not the total hydrogen count.

Unit 4: Transition and Inner Transition Elements

Electronic configuration anomalies, especially chromium and copper
Reason for variable oxidation states
Why transition metal ions are coloured
Magnetic moment calculation from the number of unpaired electrons
Lanthanoid contraction and its consequences
Preparation and properties of potassium dichromate and potassium permanganate

Unit 5: Coordination Chemistry

IUPAC naming of complexes
Types of isomerism: ionisation, linkage, coordination, geometrical and optical
Effective atomic number
Crystal field splitting, high spin versus low spin
Predicting colour and magnetic behaviour from the splitting
Chelate effect and stability

This is the highest-yield inorganic unit for one-markers. If you master one inorganic unit completely, make it this one.

Unit 6: Solid State

Number of atoms per unit cell for simple, body centred and face centred cubic
Packing efficiency values
Coordination number in each lattice type
Schottky and Frenkel defects and their effect on density
Radius ratio rules

The density effect of the two defects is the single most tested point here. Schottky lowers density, Frenkel leaves it unchanged.

Unit 7: Chemical Kinetics

Order versus molecularity
Units of the rate constant for zero, first and second order
Half life expressions and their dependence on initial concentration
Arrhenius equation and the effect of temperature
Pseudo first order reactions and why they behave that way

Rate constant unit questions are effectively free marks once you can derive the units from the rate law.

Unit 8: Ionic Equilibrium

Ostwald dilution law
Common ion effect
pH of strong and weak acids and bases
Buffer solutions and the Henderson equation
Salt hydrolysis and whether the resulting solution is acidic, basic or neutral
Solubility product and precipitation conditions

Unit 9: Electrochemistry

Kohlrausch law
Variation of molar conductivity with dilution for strong versus weak electrolytes
Nernst equation
Standard electrode potential and predicting cell feasibility
Faraday laws of electrolysis

Unit 10: Surface Chemistry

Physisorption versus chemisorption
Freundlich adsorption isotherm
Types of colloids and Tyndall effect
Hardy-Schulze rule
Emulsions and emulsifying agents
Zeolite and enzyme catalysis

Short unit, very high mark-per-hour. Do not skip it.

Units 11 to 13: Organic Chemistry

Distinguishing tests: Lucas test, iodoform test, Tollens and Fehling
Acidity order of phenols and substituted phenols
Basicity order of amines in aqueous solution
Named reactions and their products
Diazonium salt reactions and coupling
Identifying products of oxidation and reduction from the reagent

The basicity order of amines is a classic trap, because the order in aqueous solution differs from the order in the gas phase. Read which one the question asks for.

Unit 14: Biomolecules

Classification of carbohydrates, reducing versus non-reducing sugars
Glycosidic, peptide and hydrogen bonding
Primary, secondary and tertiary protein structure
Vitamins and deficiency diseases
DNA versus RNA differences

Unit 15: Chemistry in Everyday Life

Classification of drugs by action
Antiseptic versus disinfectant, including the phenol concentration example
Types of detergents
Food additives and artificial sweeteners
Types of polymers and polymerisation

Pure recall, one evening of work, and it appears every year.

How to lock this section down

Turn each bullet above into a question and answer it from memory rather than reading the list. Keep the ones you fail on a single page and revise that page daily. Chemistry rewards frequent short retrieval far more than long reading sessions.

More Class 12 material is being added on the Class 12 section.