Chemistry S & P Block Elements BUMHS 2024
PMDC Verified Question 19 of 104
Which of the following elements react rapidly with water at room temperature?
A
Cu
B
Na
C
Fe
D
Al
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: Na
Concept:

The reactivity of a metal with water is determined by its ionization energy and its position in the electrochemical series.

Solution:

  • Alkali metals (Group I-A) possess the lowest ionization energies in their respective periods, making them the most electropositive and reactive metals.
  • Sodium (Na) is an alkali metal. When placed in cold water at room temperature, it reacts vigorously and highly exothermically to form sodium hydroxide and release hydrogen gas.
  • The reaction is so rapid that the heat generated often melts the sodium metal into a sphere that darts across the water's surface.


Why other options are incorrect:

  • Cu (Copper): Very unreactive; sits below hydrogen in the reactivity series and does not react with water.
  • Fe (Iron): Only reacts with steam at very high temperatures to form iron oxide.
  • Al (Aluminum): Protected by a tough, impermeable layer of aluminum oxide (\( \text{Al}_2\text{O}_3 \)), preventing it from reacting rapidly with cold water.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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