21.

Which one of the following ionic species has the greatest proton affinity to form stable compound? 

• HS^-

• NH₂^-

• F^-

• F^-

CH₃-CHCl-CH₂-CH₃ has a chiral centre. Which one of the following represents its R configuration?

0.5 Molal aqueous solution of aweak acid (HX) is 20% ionised. If K_f for water is1.86 K kg mol^-1, the lowering in freezing point of the solution is:

• -1.12 K 

• 0.56 K 

• 1.12 K 

• 1.12 K 

The Langmuir adsorption isotherm is deduced using  the assumption: 

• the adsorption takes place in multilayers

• The adsorption sites are equivalent in their ability to adsorb the particles

• The adsorbed molecules interact with each other

• The adsorbed molecules interact with each other

The reaction of hydrogen and iodine monochloride is given as:
H₂ (g) + 2ICl (g) → 2 HCl (g)  + I₂ (g)
This reaction is of first order with respect to H₂ (g) and ICI (g), following mechanisms were proposed:

Mechanism A:
H₂ (g) + 2 ICl (g)  → 2 HCl (g) + I₂ (g) 

Mechanism B:
H₂ (g) + ICl (g) →HCl (g) + HI (g) ;slow
HI (g) + ICl (g)  → HCl (g) + I₂ (g); fast

Which of the above mechanism (s) can be consistent with the given information about the reaction? 

• B only

• A and B both

• Neither A nor B

• Neither A nor B

Which one of the following anions is present in the chain structure silicates ?

• Si₂O₇^6-

• (Si₂O₅^6-)_n

• (SiO₃^2-)_n

• (SiO₃^2-)_n

The fraction of totoal volume occupied by the atoms present in a simple cube is: 

• π/6

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• 
• 

For the following:
(i) I^-  (ii) Cl^-   (iii) Br^-

the increasing order of nucleophilicity would be: 

• I^- < Br^- < Cl^-

• Cl^- < Br^- < I^-

• I^- < Cl^- < Br^-

• I^- < Cl^- < Br^-

Which one of the following orders correctly represents the increasing acid strengths of the given acids? 

• HOCl < HOClO < HOClO₂ < HOClO₃

• HOClO < HOCl < HOClO₃ < HOClO₂

• HOClO₂ < HOClO₃ < HOClO < HOCl

• HOClO₂ < HOClO₃ < HOClO < HOCl

In a first order reaction A →B, if k israte constant and initial concentration of the reactant A is 0.5 A M then the half -life is : 

• 0.693/0.5 k

• log2/k

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