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Q150 (IAS/2002) Science & Technology › Basic Science (Physics, Chemistry, Biology) › Basic mechanics concepts Answer Verified

Assertion (A) : An iron ball floats on mercury but gets immersed in water. Reason (R) : The specific gravity of iron is more than that of mercury.

Result
Your answer: —  ·  Correct: C
Explanation

Assertion (A) is true: an iron ball will float on mercury but sink in water because flotation depends on the densities (or specific gravities) of the object and the fluid. A block of iron has density ≈7.9 g/cm³ [1], while mercury has a much higher specific gravity (≈13.6) so iron displaces a volume of mercury whose weight equals the iron’s weight with only part of the ball submerged, letting it float. Water’s density is ≈1 g/mL, much less than iron’s, so iron displaces insufficient water weight and thus sinks in water [2]. The Reason (R) claiming iron’s specific gravity is more than mercury’s is incorrect; therefore R is false and does not explain A. Archimedes’ principle underlies this density-based explanation.

Sources

  1. [1] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > Keep the curiosity alive > p. 151
  2. [2] Science ,Class VIII . NCERT(Revised ed 2025) > Chapter 9: The Amazing World of Solutes, Solvents, and Solutions > Conversion factor for density > p. 141
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