Some Basic concepts of chemistry-MCQs

These 50 multiple-choice questions are carefully designed to reinforce and assess conceptual clarity in NCERT Class XI Chemistry Chapter 1 – Some Basic Concepts of Chemistry. The chapter lays the quantitative and philosophical foundation of chemistry, introducing students to the nature of matter, laws of chemical combination, mole concept, stoichiometry, units and measurements, significant figures, and concentration terms. The MCQs progress systematically from fundamental definitions and laws to numerical reasoning, dimensional analysis, and exam-oriented problem-solving. This graded difficulty structure helps learners strengthen basics before advancing to NEET/JEE-level conceptual applications. Each question is supported with a clear explanation to promote conceptual understanding rather than rote memorization. The set is ideal for classroom practice, self-assessment, competitive exam preparation, and quick revision. By practicing these MCQs, students develop accuracy, speed, and confidence in quantitative chemistry—skills that are indispensable throughout senior secondary chemistry and beyond.

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Chemistry

CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES-Objective Questions for Entrance Exams

Ent-Exam-Mcqs • Feb 2026

These MCQs are designed to strengthen conceptual clarity and exam readiness for NCERT Class XI Chemistry – Chapter 3: Classification of Elements and...

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Ent-Exam-Mcqs
Chemistry

CLASSIFICATION OF ELEMENTS AND PERIODICITY IN PROPERTIES-Exercises

Exercise • Feb 2026

The solutions presented in this section are designed to help Class XI students develop a clear and logical understanding of NCERT Chemistry Chapter 3,...

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Exercise

Some Basic concepts of chemistry

by Academia Aeternum

1. Which of the following best defines chemistry?
(Class XI – Basic Concept)
2. Matter is anything that has:
(Class XI – Basic Concept)
3. Which of the following is a physical change?
(Class XI – Conceptual)
4. The SI unit of amount of substance is:
(Class XI – Fundamentals)
5. One mole of any substance contains:
(Class XI – Conceptual)
6. The mass of 1 mole of carbon-12 is:
(Class XI – Numerical)
7. Which law states that mass is conserved during a chemical reaction?
(Class XI – Laws of Chemistry)
8. The ratio by mass of elements in a compound is always:
(Class XI – Laws)
9. Which pair illustrates the law of multiple proportions?
(Class XI – Conceptual)
10. Atomic mass unit (amu) is defined relative to:
(Class XI – Fundamentals)
11. The average atomic mass of chlorine is 35.5 due to:
(Class XI – Isotopes)
12. Which of the following is an intensive property?
(Class XI – Properties of Matter)
13. Density is defined as:
(Class XI – Formula Based)
14. Which of the following is a derived SI unit?
(Class XI – Units)
15. The number of significant figures in 0.00520 is:
(Class XI – Significant Figures)
16. Which measurement is most precise?
(Class XI – Data Analysis)
17. The empirical formula represents:
(Class XI – Conceptual)
18. If the empirical formula mass equals molecular mass, the formula is:
(Class XI – Conceptual)
19. Molar mass of \(H_2SO_4\) is:
(Class XI – Numerical)
20. The percentage of oxygen in water is approximately:
(Class XI – Numerical)
21. One mole of any gas at STP occupies:
(Class XI – Gas Concept)
22. The number of moles in 44 g of \(CO_2\) is:
(Class XI – Numerical)
23. Which quantity has no unit?
(Class XI – Conceptual)
24. Molarity depends on:
(Class XI – Conceptual)
25. Molality is expressed as:
(Class XI – Formula)
26. Which is more reliable at varying temperatures?
(Class XI – Application)
27. Limiting reagent determines:
(Class XI – Stoichiometry)
28. In a reaction, theoretical yield is:
(Class XI – Conceptual)
29. Percentage yield is calculated as:
(Class XI – Formula)
30. The dimensional formula of density is:
(Class XI – Advanced Basics)
31. If 2 moles of \(NaOH\) react with 1 mole of \(H_2SO_4\), the balanced equation is:
(Class XI – Stoichiometry)
32. Which has the maximum number of atoms?
(Class XI – Comparative)
33. The smallest mass is of:
(Class XI – Numerical Concept)
34. A solution containing 1 mol solute in 1 L solution is:
(Class XI – Concentration)
35. The term stoichiometry refers to:
(Class XI – Conceptual)
36. Which error affects accuracy but not precision?
(Class XI – Experimental)
37. The mass percent of solute is:
(Class XI – Formula)
38. Which quantity remains unchanged on dilution?
(Class XI – Conceptual)
39. Avogadro’s law relates:
(Class XI – Gas Laws)
40. The volume occupied by 0.5 mol of gas at STP is:
(Class XI – Numerical)
41. Which is a state function?
(Class XI – Conceptual)
42. The mole fraction of solvent in a dilute solution is:
(Class XI – Reasoning)
43. The limiting reagent is the reactant:
(Class XI – Application)
44. Which measurement has highest relative error?
(Class XI – Numerical Reasoning)
45. The formula mass of \(NaCl\) refers to:
(Class XI – Ionic Compounds)
46. The term “significant figures” indicates:
(Class XI – Measurement)
47. Which conversion factor is correct?
(Class XI – Units)
48. The smallest unit that retains chemical identity is:
(Class XI – Fundamentals)
49. If empirical formula is \(CH_2\) and molar mass is 42 g mol\(^{-1}\), molecular formula is:
(Class XI – Advanced Numerical)
50. Stoichiometric coefficients in a balanced equation represent:
(NEET/JEE – Conceptual)

Frequently Asked Questions

Chemistry is the branch of science that studies composition, structure, properties, and transformations of matter.

Matter is anything that has mass and occupies space.

The SI unit is mole (mol).

One mole contains \(6.022\times10^{23}\) entities.

\(N_A = 6.022\times10^{23}\,mol^{-1}\).

\(1\,u=\frac{1}{12}\)th mass of one \(^{12}C\) atom.

Average mass of atoms relative to \(1/12\)th of \(^{12}C\).

Sum of atomic masses of all atoms in a molecule.

Sum of atomic masses in an ionic compound.

Molar mass \(=\frac{\text{Mass}}{\text{Moles}}\).

Mass of one mole of substance in g mol\(^{-1}\).

\(n=\frac{m}{M}\).

Mass percent of each element in a compound.

\(\%\text{element}=\frac{\text{mass of element}}{\text{molar mass}}\times100\)

Mass is neither created nor destroyed in a chemical reaction.

A compound always contains elements in fixed mass ratios.

Reactant consumed first, limiting product formation.

Reactant left unconsumed after reaction completion.

Quantitative relationship between reactants and products.

Simplest whole-number ratio of atoms.

Actual number of atoms in a molecule.

\(\text{Molecular formula}=(\text{Empirical formula})_n\)

\(n=\frac{\text{Molecular mass}}{\text{Empirical formula mass}}\)

Amount of solute per unit volume of solution.

\(M=\frac{\text{moles of solute}}{\text{volume in litres}}\)

Moles of solute per kg of solvent.

\(m=\frac{\text{moles}}{\text{kg solvent}}\)

Ratio of moles of component to total moles.

\(X_A=\frac{n_A}{n_A+n_B}\)

Gram equivalents per litre of solution.

\(\rho=\frac{m}{V}\)

\(M=\frac{\rho\times1000}{M_r}\)

Digits conveying measurement precision.

Non-zero digits significant; trailing zeros without decimal not significant.

Method using unit conversions to solve problems.

\(PV=nRT\)

\(8.314\,J\,mol^{-1}K^{-1}\)

Mass that reacts with or replaces 1 g H or 8 g O.

Quantitative analysis based on mass measurement.

Quantitative analysis using volume of solutions.

Process to determine concentration using standard solution.

Highly pure compound used to prepare standard solution.

Amount of product formed.

Maximum possible yield from given reactants.

\(\%\text{yield}=\frac{\text{actual}}{\text{theoretical}}\times100\)

Parts per million: \(10^{-6}\) fraction.

Closeness to true value.

Reproducibility of measurements.

Estimated range of measurement error.

\(6.022\times10^{23}\) atoms.

\(n=\frac{18}{18}=1\) mol.

\(0.5\times44=22\) g.

22.4 L (approximate school value).

Numerical factor before chemical species.

Equalizing atoms on both sides of reaction.

Substance consumed in reaction.

Substance formed in reaction.

Identification of constituents.

Determination of amount of constituents.

It connects atomic scale to laboratory scale for calculations.

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