Which of the following is not a correct statement?

1.	The electron deficient molecules can act as Lewis acids.
2.	The canonical structures have no real existence.
3.	Every AB5 molecule does in fact have square pyramidal structure.
4.	Multiple bonds are always shorter than corresponding single bonds.

Which of the following is not isostructural with SiCl₄?

1. $SC{l}_4$

2. $S{O}_4^{2-}$

3. $P{O}_4^{3-}$

4. $N{H}_4^{+}$

Which of the following diatomic molecular species has only $\mathrm{\pi }$ bonds according to Molecular Orbital Theory?

1.  Be₂

2.  O₂

3.  N₂

4.  C₂

The number of sigma ($\mathrm{\sigma }$) and pi ($\mathrm{\pi }$) bonds in pent-2-en-4-yne is:

1. 13 $\mathrm{\sigma }$ bonds and no $\mathrm{\pi }$ bond

2. 10 $\mathrm{\sigma }$ bonds and 3 $\mathrm{\pi }$ bonds

3. 8 $\mathrm{\sigma }$ bonds and 5 $\mathrm{\pi }$ bonds

4. 11 $\mathrm{\sigma }$ bonds and 2 $\mathrm{\pi }$ bonds

The correct structure of tribromo octoxide is:

Which of the molecule is not hypovalent but complete octet :

1. AlCl₃                   

2. AlBr₃

3. AlF₃                     

4. BF₃

A molecule that has a complete octet is:

 1. BeCl₂(dimer)       

 2. BeH₂(dimer)

 3. BeH₂(s)               

 4. BeCl₂(s)

Mg₂C₃ reacts with water forming propyne ${\mathrm{C}}_3^{4-}$ . The number of sigma and pie bonds in \(C_{3}^{4-}\)is-  

1. Two sigma and two pi bonds.             

2. Three sigma and one pi bonds.           

3. Two sigma and one pi bonds.          

4. Two sigma and three pi bonds.

According to Born-Haber's cycle, the enthalpy of the formation of ionic compounds can be determined. The formation of NaCl involves the following steps :

(I) \(Na(s)\xrightarrow[Energy \ of \ sublimation]{S} \ Na(g)\)     

(II) \(Na(g)\xrightarrow[Ionisation \ potential]{I} \ Na^{+}(g) \ + \ e^{-}\)

(III) \(Cl_{2}(g)\xrightarrow[Bond \ dissociation \ energy]{D} \ 2Cl(g)\)

(IV) \(Cl(g) \ + e^{-}\xrightarrow[Electron \ affinity \ energy]{E} \ Cl^{-}(g)\)

 (V) \(Cl^{-}(g) \ + Na^{+}(g)\xrightarrow[Lattice \ energy \ energy]{U} \ NaCl(s)\)

The enthalpy of formation of NaCl will be :

1. $∆{\mathrm{H}}_{\mathrm{f}}=\mathrm{S}+\mathrm{I}-\frac{\mathrm{D}}{2}-\mathrm{E}-\mathrm{U}$

2. $∆{\mathrm{H}}_{\mathrm{f}}=\mathrm{S}+\mathrm{I}+\frac{\mathrm{D}}{2}-\mathrm{E}-\mathrm{U}$

3. $∆{\mathrm{H}}_{\mathrm{f}}=-\mathrm{S}-\mathrm{I}-\mathrm{D}+\frac{E}{2}+\mathrm{U}$

4. $∆{\mathrm{H}}_{\mathrm{f}}=-\mathrm{S}-\mathrm{I}-\mathrm{D}-\frac{E}{2}-\mathrm{U}$

Which of the following is the least volatile?
     

1. HCN                     
2. HF        
3. H₂O                     
4. CS₂