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Some Basic Concepts of Chemistry — NEET & JEE MCQs with answers
Chemistry is the branch of science that studies the preparation, properties, structure, and reactions of material substances. Class 11 Chapter 1 covers the classification of matter, SI units, uncertainty in measurement, fundamental chemical laws, Dalton's atomic theory, atomic and molecular masses, the mole concept, and stoichiometric calculations. It builds the quantitative foundation on which all further chemistry rests.
Topics in this chapter
- 1.1 Importance of Chemistry
- 1.2 Nature of Matter
- 1.3 Properties of Matter and Their Measurement
- 1.4 Uncertainty in Measurement
- 1.5 Laws of Chemical Combination
- 1.6 Dalton's Atomic Theory
- 1.7 Atomic and Molecular Masses
- 1.8 Mole Concept and Molar Masses
- 1.9 Percentage Composition
- 1.10 Stoichiometry and Stoichiometric Calculations
Free practice questions
Express $0.200$ in scientific notation, preserving its significant figures.
- A. $2 \times 10^{-1}$
- B. $2.00 \times 10^{-1}$
- C. $2.00 \times 10^{1}$
- D. $2.0 \times 10^{-1}$
Show answer
Answer: B — $0.200$ has three significant figures. Moving the decimal one place right gives $2.00 \times 10^{-1}$, which retains three significant figures.
NCERT Class 11 Chemistry · Ch 1 · 1.4.1 Scientific Notation
A 0.5 mol sample of $Na_2CO_3$ has a mass of: (Molar mass $Na_2CO_3$ = 106 g)
- A. 106 g
- B. 212 g
- C. 53 g
- D. 26.5 g
Show answer
Answer: C — Mass = moles × molar mass = $0.5\times106 = 53$ g.
NCERT Class 11 Chemistry · Ch 1 · 1.10.2 (Exercise 1.25)
A compound with empirical formula $CH_2O$ (empirical formula mass 30 g) has a molar mass of 60 g. Its molecular formula is:
- A. $C_6H_{12}O_6$
- B. $CH_2O$
- C. $C_2H_4O_2$
- D. $C_3H_6O_3$
Show answer
Answer: C — n = 60/30 = 2. Molecular formula = (CH2O)2 = C2H4O2 (acetic acid).
NCERT Class 11 Chemistry · Ch 1 · 1.9 Empirical and Molecular Formulas · Problem 1.2
According to NCERT, in any quantitative measurement, the number is always followed by a unit. In the measurement '6 m', which part is the unit?
- A. 6
- B. both 6 and m
- C. neither 6 nor m
- D. m (metre)
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Answer: D — NCERT explains that in '6 m', 6 is the number and m (metre) is the unit in which the length is measured.
NCERT Class 11 Chemistry · Ch 1 · 1.3.2 Measurement of physical properties
According to the Law of Multiple Proportions, when two elements combine to form more than one compound, the masses of one element that combine with a fixed mass of the other are in the ratio of:
- A. Equal proportions by weight
- B. Small whole numbers
- C. Their atomic masses
- D. Simple ratio by volume
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Answer: B — NCERT states the masses of one element that combine with a fixed mass of the other element are in the ratio of small whole numbers.
NCERT Class 11 Chemistry · Ch 1 · 1.5.3 Law of Multiple Proportions
Which of the following does NOT appear in NCERT's list of products whose manufacture involves the principles of chemistry?
- A. Detergents
- B. Dyes
- C. Nuclear fuel rods
- D. Alloys
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Answer: C — NCERT lists 'manufacturing fertilisers, alkalis, acids, salts, dyes, polymers, drugs, soaps, detergents, metals, alloys, etc., including new material'. Nuclear fuel rods are not in this list.
NCERT Class 11 Chemistry Ch 1
Using N = 14.01 u (NCERT method), the molecular mass of nitrogen gas $N_2$ is approximately:
- A. 14.01 u
- B. 32.00 u
- C. 28.02 u
- D. 7.00 u
Show answer
Answer: C — Molecular mass of $N_2 = 2 \times 14.01 = 28.02\ \text{u}$ (NCERT 1.7.3: sum of atomic masses; $N_2$ is diatomic).
NCERT Class 11 Chemistry · Ch 1 · 1.7.3 Molecular Mass
How many moles of oxygen molecules are present in 64 g of $O_2$? (Molar mass $O_2$ = 32.00 g/mol)
- A. 2 mol
- B. 0.5 mol
- C. 1 mol
- D. 4 mol
Show answer
Answer: A — $n = \dfrac{64}{32.00} = 2\ \text{mol}$ (NCERT 1.8: moles = mass / molar mass; $O_2$ molar mass = 32.00 g/mol).
NCERT Class 11 Chemistry · Ch 1 · 1.8 (moles = mass / molar mass)
Dalton proposed the law of multiple proportions in the year:
- A. 1789
- B. 1803
- C. 1808
- D. 1811
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Answer: B — NCERT states: 'This law was proposed by Dalton in 1803.' His atomic theory followed five years later, in the 1808 publication of A New System of Chemical Philosophy.
NCERT Class 11 Chemistry Ch 1
Which of the following is given by NCERT as an example of a heterogeneous mixture?
- A. Sugar solution
- B. A mixture of salt and sugar
- C. Glucose
- D. Air
Show answer
Answer: B — NCERT gives 'mixtures of salt and sugar, grains and pulses along with some dirt (often stone pieces)' as heterogeneous mixtures. Sugar solution and air are homogeneous.
NCERT Class 11 Chemistry · Ch 1 · 1.2.2 Classification of Matter
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