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UCE (O-Level) Chemistry — practice by topic

Browse 61 questions across 56 Chemistry topics. Choose what you want to revise, then open a question to check its answer and worked solution.

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Chemistry topics

Alcohols, Phenols and Ethers (24)Alcohols Phenols Ethers (24)Aldehydes Ketones (24)Aldehydes, Ketones and Carboxylic Acids (24)Alkenes (24)Amines (24)Atomic Structure (24)Atomic Structure and Valency (24)Atoms and Molecules (24)Chemical Bonding (24)Chemical Bonding and Molecular Structure (24)Chemical Equilibrium (24)Classification of Elements (24)Classification of Elements and Periodicity (24)Classification of Elements and Periodicity in Properties (24)d- and f-Block Elements (24)Electrochemical Series (24)Equilibrium (24)Equilibrium Constant (24)Equipotential Surfaces (24)Haloalkanes and Haloarenes (24)Hydrocarbons (24)Hydrogen (24)Ideal and Non-Ideal Solutions (24)Ideal Solutions (24)Non-Ideal Solutions (24)Organic Chemistry (24)Organic Chemistry: Some Basic Principles and Techniques (24)p-Block Elements (24)p-Block Elements (Groups 15-18) (24)Periodic Classification (24)Periodic Classification of Elements (24)Periodic Table (24)Periodic Trends (24)Polymers (24)Reactions in Aqueous Solution (24)Redox & Electrochemistry (24)Redox Reactions (24)S Block Elements (24)Solid State (24)Some Basic Concepts of Chemistry (24)States of Matter (24)Surface Areas and Volumes (24)Surface Chemistry (24)Surface Tension (24)The Atom (24)The d- and f-Block Elements (24)The p-Block Elements (24)The Periodic Table (24)Atomic combinations (8)Energy and chemical change (7)Types of reactions (6)Ideal gases (5)Intermolecular forces (4)Quantitative aspects of chemical change (4)The lithosphere (3)

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How is a covalent bond between two atoms formed?Read the answer and worked solution →What name is given to the electrons in the outermost energy level of an atom?Read the answer and worked solution →An oxygen atom in a water molecule keeps two electron pairs entirely to itself. What are these pairs called?Read the answer and worked solution →In a dative covalent bond, where do the two shared electrons come from?Read the answer and worked solution →

Worked practice questions

How is a covalent bond between two atoms formed?

  1. Sharing pairs of electrons
  2. Losing pairs of electrons
  3. Gaining pairs of protons
  4. Trading pairs of neutrons
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Correct answer: A. Sharing pairs of electrons

1. Atoms bond in order to fill their outermost energy level, as the noble gases already have. 2. A covalent bond is a chemical bond where pairs of electrons are shared between two atoms. 3. The outermost orbitals overlap so that unpaired electrons from each atom can be shared. 4. Protons and neutrons sit in the nucleus and take no part in ordinary bonding. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 3: Atomic combinations_

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What name is given to the electrons in the outermost energy level of an atom?

  1. Core electrons
  2. Valence electrons
  3. Bonded electrons
  4. Paired electrons
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Correct answer: B. Valence electrons

1. An atom has a central nucleus surrounded by electrons in fixed energy levels. 2. The electrons in the outermost energy level are called the valence electrons. 3. Only these electrons take part in bonding, which is why a Lewis diagram shows them alone. 4. Electrons in the inner levels are the core electrons, so that option names the wrong group. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 3: Atomic combinations_

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An oxygen atom in a water molecule keeps two electron pairs entirely to itself. What are these pairs called?

  1. A bond pair
  2. A free pair
  3. A lone pair
  4. A spare pair
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Correct answer: C. A lone pair

1. Oxygen forms one bond with each hydrogen atom using its two unpaired electrons. 2. The remaining two pairs are not shared with any other atom. 3. An unshared electron pair is called a lone pair, and it stays on the atom it belongs to. 4. A bonding pair is shared between two atoms, which is exactly what these pairs are not. _Source: Siyavula Physical Sciences Grade 11 (Everything Science, CC BY 4.0), Chapter 3: Atomic combinations_

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