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Question
Assertion :Boron can only form [BF4]−, whereas aluminum forms [AlF6]3− Reason: The first member of a group of elements in the s− and p−blocks shows anomalous behavior
Assertion :Boron can only form [BF4]−, whereas aluminum forms [AlF6]3− Reason: The first member of a group of elements in the s− and p−blocks shows anomalous behavior
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Solution
The correct option is B Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
The maximum covalency of first member of each group of s− and p−block elements is 4, (due to nonavailability of d−orbitals) whereas the other members can expand their valence shell to accommodate more than four pairs of electrons (due to the availability of d−orbitals). In other words, in the valence shell of B, one s and three p orbitals are present. s orbital can accommodate one electron pair and three p orbitals can accommodate 3 pairs of electrons. Thus the valence shell of B can accommodate maximum 4 electron pairs. Also, in the valence shell of Al (in [AlF6]3−), six electron pairs are present which requires one s, 3 p and 2 d orbitals.
The maximum covalency of first member of each group of s− and p−block elements is 4, (due to nonavailability of d−orbitals) whereas the other members can expand their valence shell to accommodate more than four pairs of electrons (due to the availability of d−orbitals). In other words, in the valence shell of B, one s and three p orbitals are present. s orbital can accommodate one electron pair and three p orbitals can accommodate 3 pairs of electrons. Thus the valence shell of B can accommodate maximum 4 electron pairs. Also, in the valence shell of Al (in [AlF6]3−), six electron pairs are present which requires one s, 3 p and 2 d orbitals.
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