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NEET Chemistry NEET PYQ-The d-and f-Block Elements

  • question_answer
    Four successive members of the first row transition elements are listed below with their atomic numbers. Which one of them is expected to have the highest third ionization enthalpy?                                     [AIPMT (S) 2005]

    A) Vanadium (Z = 23)        

    B) Chromium (Z = 24)

    C) Iron (2 = 26)

    D) Manganese (Z = 25)

    Correct Answer: D

    Solution :

    [d] In 23V = 1s2, 2s2 2p6, 3s2 3p6 3d3, 4s2
                Third electron which is removed in third ionisation potential enthalpy belongs to 3d3 sub-shell.
                            24Cr = 1s2, 2s2 2p6, 3s2 3p6 3d6 4s2
                Third electron which is removed m third ionisation potential enthalpy belongs to 3d5 sub-shell.
                            26Fe = 1s2, 2s2 2p6, 3s2 3p6 3d6, 4s2
                Third electron which is removed in third ionisation potential enthalpy belongs to 3d6 sub-shell.
                            2SMn = 1s2, 2s2 2p6, 3s2 3p6 3d5 4s2
                Third electron which is removed in third ionisation potential belongs to 3d5 sub-shell.
                In all elements shell and sub-shells are same. Required amount of energy (enthalpy) is based upon the stability of d-subshell.
                The 3d5 sub-shell has highest stability in all because it is half filled sub-shell (while other are incomplete). So Mn shows highest third ionisation potential or enthalpy.


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