(a) XeF₄ is sp³d² hybridised with 4 bond pairs and 1 lone pair and structure is square planar. Here all the bond lengths are equal.

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 1

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 1

(b) $$\,\,\,\,$$ BF$$_4^ - $$, 4 bond pair present so angle is 109^o 28^' and sp³ hybridised. So structure is regular tetrahedral. Here all the bond lengths are equal.

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 2

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 2

(c) SF₄ is sp³d hybridised with 4 bond pairs and 1 lone pair and its expected trigonal bipyramidal geometry gets distorted due to presence of a lone pair of electrons and it becomes distorted tetrahedral or see-saw with the bond angles equal to < 120^o and 179^o instead of the expected angles of 120^o and 180^o respectively. Here axial and equitorial both bonds are presents. And we know axial bonds are longer and weaker.

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 3

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 3

(d) SiF₄ is sp³ hybridisation and regular tetrahedral geometry. Here all the bond lengths are equal.

AIEEE 2006 Chemistry - Chemical Bonding & Molecular Structure Question 210 English Explanation 4