The atomic number of the element from the following with lowest 1st ionisation...| Doubtify JEE

 

Atomic Number of the Element with Lowest First Ionisation Enthalpy | JEE Chemistry

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📌 Question

The atomic number of the element from the following with the lowest first ionisation enthalpy is:

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📚 Concept Used – First Ionisation Enthalpy

• Definition: First ionisation enthalpy is the energy required to remove the most loosely bound electron from an isolated gaseous atom in its ground state.

• Periodic Trend:

  • Across a period → IE increases (nuclear charge ↑, atomic size ↓)

  • Down a group → IE decreases (atomic size ↑, shielding effect ↑)

• Lowest IE Element: The element at the bottom-left of the periodic table has the lowest IE, because it has large size and weak nuclear attraction for the outermost electron.

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🖋 Solution

The element with the lowest first ionisation enthalpy is Francium (Fr), but in practical chemistry, Cesium (Cs) is often considered because Francium is radioactive and rare.

• Francium’s atomic number = 87

• Therefore, the answer is 87.

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✅ Final Answer: 87 (Francium)

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🖼 Image

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🎥 Final Video Solution: