NEET AIPMT SOLVED PAPER 2001

  • question_answer
                                      Correct order of Ist ionisation potential (I.P.) among following elements Be, B, C, N, O is:             

    A)                 B < Be < C < O < N           

    B)                 B < Be < C < N < O

    C)                 Be < B < C < N < O                                           

    D)                 Be < B < C < O < N

    Correct Answer: A

    Solution :

                                              Ionisation potential: The amount of energy required to remove an electron from the outer-most orbit of a gaseous atom is known as ionisation potential. Elements having half filled or completely filled orbitals are more stable than partially filled orbitals.                 In a period from left to right ionisation potential decreases as the atomic number increases. The given elements (Be, B, C, N, O) are present in II period as                 \[\xrightarrow[\text{Ionisation potential increases}]{Be\,\,\,\,\,\,\,\,\,B\,\,\,\,\,\,\,\,C\,\,\,\,\,\,\,N\,\,\,\,\,\,\,O}\]                 But in case of Be and B, 'Be' has higher ionisation potential due to stable configuration.                 \[_{4}Be=1{{s}^{2}},\,2{{s}^{2}}\]                 \[\] Stable configuration                 \[_{5}B=1{{s}^{2}},2{{s}^{2}},2{{p}^{1}}\]                 \[\] Unstable configuration                 In the same way in case of 'N' and 'O', 'N? has higher I.P. than 'O' due to stable configuration                 \[\begin{align}   & _{7}N=1{{s}^{2}},2{{s}^{2}}2{{p}^{3}} \\  & \,Stable\,configuration \\ \end{align}\]                 \[\begin{align}   & _{8}O=1{{s}^{2}},2{{s}^{2}}2{{p}^{4}} \\  & \,Unstable\,\,configuration \\ \end{align}\]                 So, the correct order of increasing IP will be:                 B < Be < C < O < N.


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