Chemistry Exam Past Questions and Answers | JAMB, WAEC and NECO

Chemistry is the study of the substances that make up matter. It looks at their properties, how they react with each other, and how these reactions can create new substances.

• Question 1241: A substance S is isomorphous with another substance R. When a tiny crystals of S is added into a supersaturated solution of R? Options:
  A) S dissolves in the solution
  B) crystals of R are precipitated
  C) there is no observable change
  D) R and S react to generate heat
  Show Answer
  The correct answer is B .
• Question 1242:

  Which of the following is a physical change?

  Options:
  A) Exposing white phosphorus to air
  B) Burning kerosene
  C) Dissolving calcium in water
  D) Freezing ice cream
  Show Answer
  The correct answer is D .
• Question 1243:

  An aqueous solution of a metal salt, M. gives a white precipitate with NaOH which dissolves in excess NaOH. With aqueous ammonia, the solution of M also gives a white precipitate which dissolves in excess ammonia Therefore the cation in M is

  Options:
  A) Zn
  B) Ca
  C) Al
  D) Po
  Show Answer
  The correct answer is A .
• Question 1244: Which of the following electrodes is used in electrolysis of bauxite (Al₂O₃) in molten cryolite? Options:
  A) Steel electrodes
  B) Carbon electrodes
  C) Mercury electrodes
  D) Carbon anode and steel cathode
  E) Carbon cathode and stell anode
  Show Answer
  The correct answer is B .
• Question 1245: The condition required for corrosion to take place is the presence of Options:
  A) water and carbon (IV) oxide
  B) water, carbon (IV) oxide and oxygen
  C) oxygen and carbon (IV) oxide
  D) water and oxygen
  Show Answer
  The correct answer is D .
• Question 1246: Oxygen is a mixture of two isotopes O and O with relative abundances of 90% and 10% respectively. The relative atomic mass of oxygen is? Options:
  A) 16.0
  B) 16.2
  C) 17.0
  D) 18.0
  Show Answer
  The correct answer is B .
• Question 1247: In which of the following is the oxidation number of sulphur equal to -2? Options:
  A) SO₃
  B) S₈
  C) H₂S
  D) SO₂
  Show Answer
  The correct answer is C .
• Question 1248: The component of an atom that contributes least to its mass is the Options:
  A) proton
  B) nucleus
  C) neutron
  D) electron
  Show Answer
  The correct answer is D .
• Question 1249: Sulphur exists in six forms in the solid state. This property is known as? Options:
  A) isomerism
  B) allotropy
  C) isotopy
  D) isomorphism
  Show Answer
  The correct answer is B .
• Question 1250:

  Which of the following salts when dissolved in water will NOT give the corresponding pH value?

  Options:
  A) NaHSO₄, pH < 5
  B) Na₂CO₃, pH > 8
  C) Na₂Cl,pH = 7
  D) NaHCO, pH < 6
  Show Answer
  The correct answer is D .