A polar bond is one in which the electrons are not shared equally due to differences in electronegativities of the covalently bonded atoms.

Explanation  ;

 In many molecular compounds one atom attracts the shared pair of electrons ( or , bonding electrons ) more strongly than the other .

For example in a molecule of  HF , Fluorine (F)  attracts electrons more strongly than  hydrogen (H) . Thus the electron density at Fluorine end is more than that of the hydrogen end, represented as  under -

        H^{{tex}\delta +{/tex}} - F ^{{tex}\delta -{/tex}}

 {tex}\therefore{/tex}   H-F  bond is a polar covalent bond.

Reduction of a nitro alkane with iron scrap  (Fe)  +  HCl is preferred because ,

(i)  Fe Cl₂ is produced which gets easily hydrolysed to form FeCl₃ and release HCl during the reaction.

Fe   +    2HCl   ------------>   FeCl₂  +   2H 

(ii)  the process , therefore , becomes  economical as only a small amount of HCl  is required to initiate the reaction.

   Usually(, Fe +  HCl ) is preferred as a reducing agent , particularly in manufacture of amines.

No . 

Explanation  :       

   It is because of ,

(i)  different values of frequency factor ( A ) and effectiveness of colisions for  different for different  reaction , and  

(ii) the rate constant k is proportional to A.

Methylbromide gives both methane and ethane

The order of reaction representing rate law  as  ,

Rate  =   k  [ COCl₂ ]^3/2   is  1.5

{tex}\therefore{/tex}The unit for the rate constant  is   M ^-0.5 s^-1 

(where M represents  mole per litre or Molarity of the reactant ) 

   * It should  be noted that even though it is a gas phase reaction , where the change in pressure is conveniently measured during the course of a reaction , but still the rate constant is expressed in terms of change in concentration of the reactant  ( as per rate law ) in terms of moles per Litre (ie .M or molarity ) / unit of time .  The reason being that pressure is temperature as well as  unit dependent , where as concentration or molarity is always in moles per litre .

** The concentration of the reactant is easily calculated using  the relation  PV  =  nRT , or P  = ( n/V ) RT  

ie .   P  =  C RT     

 Explanation : 

THe unit for rate constant of a reaction is derived through dimensional analysis .

In this case since ,

 k  = Rate / [ A ] ⁿ 

(where ,  n  represents the order of reaction  

 k =Rate / [ COCl₂ ]^3/2

or,=  Rate /  [ COCl₂ ]^1.5

= ( concentration / time )  x  1 / (  concentration )^1.5 

= ( mol L^-1 ) s^-1 x  1 / ( mol L^-1 )^1.5 

=  [ ( mol L^-1 / { mol L^-1  ) x ( 1 / mol L^-1 )^0.5  }s^-1 

={ ( 1 / M )^0.5 } s ^-1 

or , =  M ^-0.5 s^-1 

[  where , mol L ^-1  , represents  molarity (M) of the reactant ]

In presence of moisture, PCl₃ and PCl₅ hydrolyses to form HCl which fumes in air. The reaction is as follows:

PCl₃ + 3H₂O -------> H₃PO₃ + 3HCl
PCl₅ + 4H₂O ------> H₃PO₄ + 5 HCl

It is estimated with the help of potassium iodide , when ozone and potassium iodide react, iodine is liberated, now this iodine is titrated against a stand solution of sodium thiosulphate using starch as an indicator.