This is because hybrid orbitals of carbon involved in ocerlapping with 1s-orbital of hydrogen are Sp³,Sp² and sp respectively and their sizes are in the order Sp³>Sp²>Sp

There is greater intermolecular hydrogen bonding in H₂ O than that in HF as each H₂ O molecule forms four H-bonds with water molecules,, whereas HF forms only H-bonds with other HF molecules. Greater the intermolecular H-bonding, greater is the viscosity. Hence, HF is less viscous than  H₂ O

This is due to greater repulsion on the axial bond pairs by the equatorial bond pairs of electrons.

Isoelectronic species are those species have same number of electrons but different nuclear charge.
Electrons present in CO = 6 + 8 = 14
Then, In NO⁺  = 7 + 8 -1 = 14
In N₂ = 7 + 7 = 14
In SnCl₂ = (very high)50 + 17 \(\times \) 2 = 50 + 34 = 84
In \({ NO }_{ \overline { 2 } }\) = 7 + 16 + 1 = 24

Bond order is defined as one half the difference between the number of electron present in the bonding and anti-bonding orbitals, i.e
Bond order (BO) \(=\frac { 1 }{ 2 } ({ N }_{ b }-{ N }_{ a })\)
A positive bond order means a stable molecule while a negative or zero bond order means an unstable molecule.
Stability of a molecule \(\propto \) bond order
Bond length \(\propto \) \(\frac { 1 }{ bond \ order } \)
Bond order values 1,2 or 3 corresponding to single, double or triple bonds respectively.

(a) AgI is more covalent that AgCl. This is because I^- ion is larger in size than Cl^- ion and hence, is more polarised than Cl ion.^-
(b) BeCl₂ is more covalent than MgCl₂ . This is because Be²⁺ ion is smaller in size than Mg²⁺ ion and hence has the greater polarising power.
(c) SnCl₄ is more covalent than SnCl₂ . This is because Sn⁴⁺ ion has greater charge and smaller size than Sn²⁺ ion and hence has greater polarising power.
(d) CuS is more covalent than CuO. This is because S^2- ion has larger size than O^2- ion and hence is more polarised than O^2- ion.

(i) In BF₃, B-atom undergoes sp² hybridisation. Hence, BF₃ is triangular planar. In NH₃, N-atom undergoes sp³ hybridisation. Hence, NH₃ has pyramidal shape with one lone pair on N-atom.
(ii) Both C in CCl₄ and Si and SiCl₄ undergo sp³ hybridisation. Hence, they are tetrahedral.
(iii) This is because of lower electronegativity of S as compared to O.

Lewis structure of CO₃^2- ion is
      
The formal charge on
(a) the carbon atom = V - L - \(\frac { 1 }{ 2 } \)S
= 4 - 0 - \(\frac { 1 }{ 2 } \)(8) = 0
(b) the oxygen atom marked as (1) = V - L - \(\frac { 1 }{ 2 } \)S
= 6 - 4 - \(\frac { 1 }{ 2 } \)(4) = 0
(c) the oxygen atoms marked as (2) and (3) = V - L - \(\frac { 1 }{ 2 } \)S
= 6 - 6 - \(\frac { 1 }{ 2 } \)(2) = -1