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 691: The pair of metals in the reactivity series that are usually extracted by the electrolysis of their ores is Options:
  A) magnesium and zinc
  B) magnesium and calcium
  C) copper and zinc
  D) lead and calcium
  Show Answer
  The correct answer is B .
• Question 692:

  What are the possible oxidation numbers of an element if its atomic number is 17?

  Options:
  A) -1 and 7
  B) -1 and 6
  C) -3 and 5
  D) -2 and 6
  Show Answer
  The correct answer is A .
• Question 693: The normal boiling point of a liquid is defined as Options:
  A) the temperature at which its vapour pressure equals the atmospheric pressure
  B) the temperature at which bubbles begin to form
  C) the temperature at which the vapour pressure equals 1 temperature
  D) the temperature at which the rate of condensation of vapour equals the rate of vaporisation of the liquid
  E) the temperature at which the space above the liquid is saturated
  Show Answer
  The correct answer is C .
• Question 694: Which of the following allotrope of carbon is a constituent of a lead pencil? Options:
  A) Graphite
  B) Diamond
  C) Lampblack
  D) Soot
  Show Answer
  The correct answer is A .
• Question 695: PCL5(g)= PCL3(g) + Cl2(g)In the reaction above, a decrease in pressure will Options:
  A) Decelerate the reaction
  B) Increase yield of Pcl3
  C) Increase the yield of Pcl5
  D) Accurate the reaction
  Show Answer
  The correct answer is B .
• Question 696: If the change in free energy of a system is -899 Jmol^-1 and the entropy change is 10Jmol^-1k^-1 at 250C, calculate the enthalpy change. Options:
  A) +2081 Jmol^-1
  B) -2081 Jmol^-1
  C) -649 Jmol^-1
  D) +649 Jmol^-1
  Show Answer
  The correct answer is A .
• Question 697: Hydrogen can be displaced from a lot alkaline solution by Options:
  A) Fe
  B) Cu
  C) Cn
  D) Sn
  Show Answer
  The correct answer is A .
• Question 698: A phenomenon where an element exist in different forms in the same physical state is known as Options:
  A) isomerism
  B) amorphism
  C) allotropy
  D) isotopy
  Show Answer
  The correct answer is C .
• Question 699: A particle that contains 8 proton, 9 neutrons and 7 electrons could be written as? Options:
  A) O
  B) O⁺
  C) O⁺
  D) O^-
  Show Answer
  The correct answer is B .
• Question 700: What is the valence shell electron configuration of the element with atomic number 17? Options:
  A) 1s² 2s² 2p⁶ 3s² 3p⁴
  B) 1s² 2s² 2p⁶ 3s² 3p⁵
  C) 2s² 2p⁶
  D) 3s² 3p⁵
  Show Answer
  The correct answer is B .