Why are basic concepts of chemistry important for NEET and JEE?

This chapter forms the foundation of Physical Chemistry. Concepts like the Mole Concept, Stoichiometry, and Concentration terms are applied across almost every other chapter in Class 11 and 12 Chemistry.

What is the molar volume of an ideal gas at STP?

The molar volume of an ideal gas at old STP (1 atm, 273.15 K) is 22.4 Liters. Under new STP (1 bar, 273.15 K), it is 22.7 Liters.

Fast-track your JEE & NEET preparation! Review the 25 most critical one-word questions, answers, and quick facts from Class 11 Chapter 1: Some Basic Concepts of Chemistry.

Basic Concepts of Chemistry: Top 25 One-Word Questions & Answers

Chapter 1 of Class 11 Chemistry, "Some Basic Concepts of Chemistry", is the bedrock of your entire competitive exam preparation. Whether you are aiming for JEE Main, JEE Advanced, or NEET, mastering the Mole Concept, Gas Laws, and Stoichiometry is non-negotiable.

To help you memorize key facts instantly, we have compiled a high-yield list of 25 one-word questions and answers. We've also added "Quick Facts" to each answer to deepen your conceptual clarity for assertion-reasoning questions!

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I. Atomic Structure & Fundamental Particles

1. Smallest particle of an element that takes part in a chemical reaction?
→ Atom
Quick Fact: Atoms may or may not exist independently, but molecules always have independent existence.
2. The total number of protons present in the nucleus of an atom?
→ Atomic Number (Z)
Quick Fact: It determines the chemical identity and the position of the element in the periodic table.
3. The sum of the number of protons and neutrons in a nucleus?
→ Mass Number (A)
Quick Fact: Protons and neutrons together are known as nucleons.
4. Atoms of the same element having different mass numbers?
→ Isotopes
Quick Fact: They have identical chemical properties but differ slightly in physical properties.
5. Atoms of different elements having the same mass number?
→ Isobars
Quick Fact: Example: Argon-40 and Calcium-40.
6. Atoms of different elements having the same number of neutrons?
→ Isotones
Quick Fact: Calculated as (A - Z) being equal for different atoms.
7. A positively charged ion formed by the loss of electrons?
→ Cation
Quick Fact: Cations are always smaller in size than their parent neutral atoms.
8. A negatively charged ion formed by the gain of electrons?
→ Anion
Quick Fact: Anions are always larger in size than their parent neutral atoms.

II. Mole Concept & Stoichiometry

9. The fundamental SI unit for the amount of substance?
→ Mole
Quick Fact: 1 mole is exactly equal to the number of atoms in 12 grams of pure Carbon-12.
10. The exact number of particles present in 1 mole of a substance?
→ Avogadro’s Number
Quick Fact: The accepted value is 6.022 × 10²³ particles/mol.
11. Standard formula to calculate the number of moles given mass?
→ n = Mass / Molar Mass
Quick Fact: Molar mass is typically expressed in g/mol.
12. The standard unit used to express atomic and molecular masses?
→ amu (or 'u')
Quick Fact: 1 amu is exactly 1/12th the mass of a Carbon-12 atom (1.66 × 10^-24 g).
13. The simplest whole-number ratio of atoms in a compound?
→ Empirical Formula
Quick Fact: For example, the molecular formula of Glucose is C₆H₁₂O₆, but its empirical formula is CH₂O.
14. What is the empirical formula of Benzene (C₆H₆)?
→ CH
Quick Fact: Dividing the molecular formula by the common factor 6 gives CH.
15. The ratio of actual mass produced in a reaction to the theoretically calculated mass?
→ Percentage Yield
Quick Fact: Formula: (Actual Yield / Theoretical Yield) × 100. It is never 100% in real-world labs.
16. The volume occupied by 1 mole of an ideal gas at old STP?
→ 22.4 L
Quick Fact: At the new standard of 1 bar pressure, it is 22.7 L.

III. Laws of Chemical Combination & Constants

17. Which law states that mass can neither be created nor destroyed in a chemical reaction?
→ Law of Conservation of Mass
Quick Fact: Given by Antoine Lavoisier. It is the basis for balancing chemical equations.
18. Which law states a chemical compound always contains exactly the same proportion of elements by mass?
→ Law of Definite Proportions
Quick Fact: Also known as Proust's Law. Pure water always has H and O in a 1:8 mass ratio.
19. Which law explains the formation of CO and CO₂ from Carbon and Oxygen?
→ Law of Multiple Proportions
Quick Fact: Proposed by John Dalton. Masses of one element that combine with a fixed mass of another are in a simple whole-number ratio.
20. Value of the Universal Gas Constant (R) in SI units?
→ 8.314 J/(mol·K)
Quick Fact: In liter-atmospheres, it is 0.0821 L·atm/(mol·K).
21. The pH value of pure, neutral water at 25°C?
→ 7
Quick Fact: Note that the neutral pH shifts slightly below 7 if the temperature is increased.
22. The name of the scientist who proposed the first scientific Atomic Theory?
→ John Dalton
Quick Fact: Proposed in 1808, stating atoms are indivisible (later disproved by discovery of subatomic particles).

IV. Elements & General Chemistry

23. The lightest and first element in the modern periodic table?
→ Hydrogen (H)
Quick Fact: It has three isotopes: Protium, Deuterium, and Tritium.
24. The only metal that exists as a liquid at standard room temperature?
→ Mercury (Hg)
Quick Fact: Widely used in traditional thermometers and barometers.
25. The only non-metal that exists as a liquid at standard room temperature?
→ Bromine (Br)
Quick Fact: It is a reddish-brown, highly volatile liquid in Group 17 (Halogens).

Why These One-Word Questions Matter for NEET & JEE

These targeted one-word questions zero in on the most scoring portion of Class 11 Chemistry. They aid in:

Quick Memory Recall: Flashcard-style learning cements facts in your active memory.
Assertion-Reason Accuracy: Knowing exact definitions helps you tackle tricky A-R questions in AIIMS/NEET.
Stoichiometry Speed: Rapid recall of formulas (like n = m/M) saves vital seconds during tough numericals.

Frequently Asked Questions (FAQs)

Why are basic concepts of chemistry important?

Chapter 1 forms the mathematical foundation of Physical Chemistry. Concepts like molarity, empirical formulas, and limiting reagents are applied continuously across Electrochemistry, Solutions, and Thermodynamics in Class 12.

How can I memorize atomic masses easily?

Focus on memorizing the first 30 elements of the periodic table, plus common halogens (Cl, Br, I) and noble metals. Practice numericals regularly—the repetitive use of masses (like Carbon = 12, Oxygen = 16, Na = 23) will naturally commit them to your memory.

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Basic Concepts of Chemistry – 25 One-Word Questions & Answers for JEE/NEET