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NEET Sample Paper NEET Sample Test Paper-93

  • question_answer
    Values of dissociation constant, \[{{K}_{a}}\] are given as follows:
    Acid \[{{K}_{a}}\]
    HCN \[6.2\times {{10}^{-10}}\]
    HF \[7.2\times {{10}^{-4}}\]
    \[HN{{O}_{2}}\] \[4.0\times {{10}^{-4}}\]
    Correct order of increasing base strength of the base \[C{{N}^{-,}}\]\[{{F}^{-}}\] and \[NO_{2}^{-}\] will be:

    A) \[{{F}^{-}}<C{{N}^{-}}<NO_{2}^{-}\]

    B) \[NO_{2}^{-}<C{{N}^{-}}<{{F}^{-}}\]

    C) \[{{F}^{-}}<NO_{2}^{-}<C{{N}^{-}}\]

    D) \[NO_{2}^{-}<{{F}^{-}}<C{{N}^{-}}\]

    Correct Answer: C

    Solution :

    [c] Higher the value of \[{{K}_{a}}\] lower will be the value of \[p{{K}_{a}}\]i.e. higher will be the acidic nature. Further since \[C{{N}^{-}},\]\[{{F}^{-}}\] and \[N{{O}_{2}}^{-}\] are conjugate base of the acids HCN, HF and\[HN{{O}_{2}}\] respectively hence the correct order of base strength will be \[{{F}^{-}}<N{{O}_{2}}^{-}<C{{N}^{-}}\] (\[\therefore \] stronger the acid weaker will be its conjugate base)


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