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Grade 12 Chemistry entrance exam, 2018 E.C. (2026)

Real questions from the Grade 12 university entrance exam in Chemistry, as students sat it in 2018 E.C. Every question comes with the correct answer and a worked explanation.

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  • Natural science stream

    Who sits it

  • 2018 E.C. (2026)

    Exam year

  • 75 questions with answers

    In this set

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Answer each question yourself before opening the answer. The explanations point to the exact place in the textbook, so you know which page to reread when you miss one.

Question 1

Which of the following sub atomic particle is used to determine chemical properties of elements?

  1. A.proton
  2. B.electron
  3. C.Nucleus
  4. D.Neutron
Show the answer and explanation

Answer: B electron

Why

Electrons, particularly valence electrons in the outermost shell, are involved in chemical bonding and reactions, and therefore determine the chemical properties of elements.

Question 2

An element has two isotopes with masses of 62.93 amu (69.17%) and 64.93 amu (30.83%). What is the average atomic mass?

  1. A.64.54 amu
  2. B.63.54 amu
  3. C.63.93 amu
  4. D.64.93 amu
Show the answer and explanation

Answer: B 63.54 amu

Why

The average atomic mass is calculated as (62.93 amu * 0.6917) + (64.93 amu * 0.3083) = 43.53 + 20.02 = 63.55 amu, which rounds closely to 63.54 amu.

Question 3

What is the effect of increasing atomic size on electronegativity down a group of periodic table?

  1. A.The electronegativity increases because the atomic energy level increases.
  2. B.The electronegativity increases because the atomic number increases.
  3. C.The electronegativity decreases because the atomic size increases.
  4. D.The electronegativity decreases because the atomic size decreases.
Show the answer and explanation

Answer: C The electronegativity decreases because the atomic size increases.

Why

As you go down a group, atomic size increases due to the addition of electron shells, which increases the distance between the nucleus and valence electrons, thereby decreasing the electronegativity.

Question 4

The periodic table contains two separate rows of inner transition elements located below the main table. These rows contain 14 elements each and belong to the 6th and 7th periods. Based on their position and electron configurations, which pair of element series correctly corresponds to 6th and 7th periods?

  1. A.Halogenes, Nobel gas
  2. B.lanthanoids, actinoids
  3. C.chalcogens, halogens
  4. D.actinoids, halogens
Show the answer and explanation

Answer: B lanthanoids, actinoids

Why

The lanthanoids (atomic numbers 57 to 71) belong to the 6th period, while the actinoids (atomic numbers 89 to 103) belong to the 7th period, and both series are placed below the main periodic table.

Question 5

Aluminum reacts with a certain nonmetallic element, X to form a compound with the general formula AlX. Element X is a diatomic gas at room temperature. Element X must be

  1. A.sulfur
  2. B.fluorine
  3. C.Bromine
  4. D.Nitrogen
Show the answer and explanation

Answer: D Nitrogen

Why

Aluminum has a +3 oxidation state, so for the neutral 1:1 compound AlX, X must have a -3 oxidation state. Nitrogen (N) is a diatomic gas (N2) at room temperature and typically forms a -3 nitride ion, yielding AlN.

Question 6

Ammonium ion (NH₄⁺) is formed when ammonia (NH₃) reacts with a hydrogen ion (H⁺). Which statement correctly analyzes the bond formed in the ammonium ion (NH₄⁺)?

  1. A.All N–H bonds are ionic because the ion carries an overall positive charge.
  2. B.N–H bond is formed when nitrogen donates a lone pair of electrons to a hydrogen ion.
  3. C.N–H bonds are formed by transfer of electrons from hydrogen to nitrogen atom
  4. D.The positive charge causes all bonds in the ion to become nonpolar covalent bonds.
Show the answer and explanation

Answer: B N–H bond is formed when nitrogen donates a lone pair of electrons to a hydrogen ion.

Why

The ammonium ion (NH4+) is formed via a coordinate covalent bond where the nitrogen atom of ammonia donates its lone pair of electrons to the empty orbital of a hydrogen ion (H+).

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Chemistry papers from other years

2017 E.C. (2025)2016 E.C. (2024)2015 E.C. (2023)2014 E.C. (2022)2013 E.C. (2021)2012 E.C. (2020)2011 E.C. (2019)2010 E.C. (2018)2009 E.C. (2017)2008 E.C. (2016)2007 E.C. (2015)2006 E.C. (2014)2005 E.C. (2013)

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Are these the real 2018 E.C. Chemistry entrance exam questions?

Yes. They come from the national university entrance exam in Chemistry that students sat in 2018 E.C. (2026). Our set holds 75 of its questions, each with its answer and an explanation that points back to the textbook.

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Can I download the Chemistry 2018 E.C. paper as a PDF?

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