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WAEC Chemistry 2025 Objective — Question 6

Question 6 of 50 from the West African Examinations Council (WAEC) Chemistry 2025 Objective paper, with the correct answer and a full explanation.

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If a gas occupies a volume of 400cm3 at a temperature of 400 K and a pressure of 1 atm, at what temperature and pressure would its volume be 200 cm3?

  • A. 800 K and 1 atm
  • B. 800 K and 0.5 atm
  • C. 200 K and 1 atmCorrect
  • D. 200 K and 0.5 atm

Explanation

Using the combined gas law, P1V1/T1 = P2V2/T2, with P1=1 atm, V1=400 cm3, T1=400 K, V2=200 cm3. Testing each option, only P2=1 atm and T2=200 K makes both sides equal: (1x400)/400 = (1x200)/200 = 1.

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