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JEE MainChemistryClassification of Elements and Periodicity in Properties

The first ionization enthalpies ( _ i H ) and electron gain enthalpies ( _ eg H ) of four elements W, X, Y and Z are given below: Element _ i H (kJ mol ⁻¹ ) _ eg H (kJ mol ⁻¹ ) W 1681 -328 X 1256 -349 Y 520 -60 Z 496 -53 If these elements correspond to Li , Na , F and Cl (not necessarily in that order), identify the correct assignment.

Options

  1. AW = F , X = Cl , Y = Li , Z = Na
  2. BW = Cl , X = F , Y = Li , Z = Na
  3. CW = F , X = Cl , Y = Na , Z = Li
  4. DW = Cl , X = F , Y = Na , Z = Li

Correct answer

A. W = F , X = Cl , Y = Li , Z = Na

Step-by-step solution

Elements with high ionization enthalpy and highly negative electron gain enthalpy belong to halogens (W and X). Elements with low ionization enthalpy and slightly negative electron gain enthalpy belong to alkali metals (Y and Z). Among halogens, F has a higher ionization enthalpy than Cl , but Cl has a more negative electron gain enthalpy than F due to interelectronic repulsions in the small 2p subshell of F . Thus, W is F and X is Cl . Among alkali metals, ionization enthalpy decreases down the group. Thus, Li has

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