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 251: In which of the following is the oxidation state of oxygen different from its value in water? Options:
  A) OH^-
  B) H₃O⁺
  C) O^-
  D) H₂O₂
  E) SO₂
  Show Answer
  The correct answer is D .
• Question 252: How many moles of (H+) are there in 1 dm³ of 0.5 M solution of H₂SO₄? Options:
  A) 2.0 moles
  B) 1.0 moles
  C) 0.5 mole
  D) 0.25 mole
  Show Answer
  The correct answer is B .
• Question 253: Bronze is an alloy of Options:
  A) copper, zinc and nickel
  B) aluminium and copper
  C) copper and zinc
  D) tin and zinc
  E) tin and copper
  Show Answer
  The correct answer is E .
• Question 254: The four classes of hydrocarbons are? Options:
  A) ethane, ethene, ethyne and benzene
  B) alkanes, alkenes, alkynes and aromatics
  C) alkanes, alkenes, alkynes and benzene
  D) methane, ethane , propane and butane
  Show Answer
  The correct answer is B .
• Question 255:

  A compound contains 31.91% potassium, 28.93% chlorine and the rest oxygen. What is the chemical formula of the compound?

  [K = 39, Cl = 35.5, O = 16]

  Options:
  A) KClO₄
  B) KClO
  C) KClO₂
  D) KClO₃
  Show Answer
  The correct answer is D .
• Question 256: When sugar is dissolved in tea, the reaction is always accomplished by Options:
  A) positive change
  B) negative entropy change
  C) no entropy change
  D) a minimum entropy change
  Show Answer
  The correct answer is C .
• Question 257: In which of the following is the oxidation number of sulphur equal to -2? Options:
  A) S₈
  B) H₂S
  C) SO ₂
  D) SO ₃^2-
  Show Answer
  The correct answer is B .
• Question 258: In which of the following pairs of element is allotropy exhibited by each element? Options:
  A) Phosphorus and hydrogen
  B) Oxygen and chlorine
  C) Sulphur and nitrogen
  D) Oxygen and sulphur
  Show Answer
  The correct answer is D .
• Question 259: 100 cm³ of oxygen is made to react with 50 cm ³ of hydrogen, and the whole reaction mixture was then passed through anhydrous calcium chloride. What is the volume of gas left? Options:
  A) 5 cm³
  B) 25 cm³
  C) 50 cm³
  D) 75 cm³
  E) 100 cm³
  Show Answer
  The correct answer is D .
• Question 260: How many lone pairs of electron are there on the central atom of the H₂O molecules? Options:
  A) 1
  B) 2
  C) 3
  D) 4
  Show Answer
  The correct answer is B .