Q 1 :    

Identify the incorrect statement from the following.           [2024]

  • The acidic strength of HX (X = F, Cl, Br and I) follows the order : HF>HCl>HBr>HI.

     

  • Fluorine exhibits –1 oxidation state whereas other halogens exhibit +1, +3, +5 and +7 oxidation states also.

     

  • The enthalpy of dissociation of F2 is smaller than that of Cl2.

     

  • Fluorine is stronger oxidising agent than chlorine.

     

(1)

As the size of X increases down the group, H–X bond strength decreases and so the acid strength increases as HF<HCl<HBr<HI.

 



Q 2 :    

Statement I : Acid strength increases in the order given as HF << HCl << HBr << HI.

Statement II : As the size of the elements F, Cl, Br, I increases down the group, the bond strength of HF, HCl, HBr, and HI decreases and so the acid strength increases.

In the light of the above statements, choose the correct answer from the options given below.               [2021]

  • Statement I is incorrect but statement II is true.

     

  • Both statement I and statement II are true.

     

  • Both statement I and statement II are false.

     

  • Statement I is correct but statement II is false.

     

(2)

 



Q 3 :    

In which one of the following arrangements the given sequence is not strictly according to the properties indicated against it?            [2021]

  • CO2<SiO2<SnO2<PbO2 : Increasing oxidizing power

     

  • HF<HCl<HBr<HI : Increasing acidic strength

     

  • H2O<H2S<H2Se<H2Te : Increasing pKa values

     

  • NH3<PH3<AsH3<SbH3 : Increasing acidic character

     

(3)

Compound              pKa
H2O 14
H2S 7
H2Se 3.872
H2Te 2.6

 



Q 4 :    

Which of the following statements is not true for halogens?               [2018]

  • All form monobasic oxyacids.

     

  • All are oxidizing agents.

     

  • All but fluorine show positive oxidation states.

     

  • Chlorine has the highest electron-gain enthalpy.

     

(3)

All halogens show both positive and negative oxidation states while fluorine shows only negative oxidation state except +1 in HOF.

 



Q 5 :    

Which one of the following orders is correct for the bond dissociation enthalpy of halogen molecules?          [2016]
 

  • Br2>I2>F2>Cl2

     

  • F2>Cl2>Br2>I2

     

  • I2>Br2>Cl2>F2

     

  • Cl2>Br2>F2>I2

     

(4)

The order of bond dissociation enthalpy is:

Cl2>Br2>B.E. (in kJ mol-1)242.6192.8F2>I2158.8151.1

A reason for this anomaly is the relatively large electron–electron repulsion among the lone pairs in F2 molecule where they are much closer to each other than in case of Cl2.

 



Q 6 :    

The variation of the boiling points of the hydrogen halides is in the order HF>HI>HBr>HCl. What explains the higher boiling point of hydrogen fluoride?       [2015]

  • There is strong hydrogen bonding between HF molecules.

     

  • The bond energy of HF molecules is greater than in other hydrogen halides.

     

  • The effect of nuclear shielding is much reduced in fluorine which polarises the HF molecule.

     

  • The electronegativity of fluorine is much higher than for other elements in the group.

     

(1)

HF forms strong intermolecular H-bonding due to high electronegativity of F. Hence, the boiling point of HF is abnormally high. Boiling points of other hydrogen halides gradually increase from HCl to HI due to increase in size of halogen atoms from Cl to I which further increase the magnitude of van der Waals’ forces.