In an octahedral structure, the pair of d orbitals involved in d²sp³-hybridisation is:

1. $d_{x^2-y^2}, d_{z^2}$

2. $d_{xy}, d_{x^2\mathit{-}{y}^{\mathit{2}}}$

3. $d_{{\mathrm{z}}^2}, d_{xz}$

4. $d_{xy}, d_{yz}$

The correct order of  bond angle order is 

(1) ${\mathrm{NH}}_2^{-}>{\mathrm{NH}}_3 >{\mathrm{NH}}_4^{+}$

(2) ${\mathrm{NH}}_4^{+}>{\mathrm{NH}}_3 >{\mathrm{NH}}_2^{-}$

(3) ${\mathrm{NH}}_3^{}>{\mathrm{NH}}_{{}_2}^{-} >{\mathrm{NH}}_4^{+}$

(4) ${\mathrm{NH}}_3^{}>{\mathrm{NH}}_4^{+} >{\mathrm{NH}}_2^{-}$

The number of sigma bonds in P₄O₁₀ is 

1. 6

2. 16

3. 20

4. 7

Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?

1. Cl₂ > Br₂ > F₂ > I₂

2. Br₂ > I₂ > F₂ > Cl₂

3. F₂ > Cl₂ > Br₂ > I₂

4. I₂ > Br₂ > Cl₂ > F₂

Which one of the following molecules contain no $\mathrm{\pi }$ -bond?

1. CO₂

2. H₂O

3. SO₂

4. NO₂