Answer:
(a) Corrosion is the oxidative deterioration of a metal, such as conversion
of iron to rust
the
tarnishing of silver (due to the formation of 
), development
of a green coating on copper and bronze.
Corrosion is basically an
electrochemical phenomenon. A metal is oxidised by loss of electrons to oxygen,
and forms metal oxides. Corrosion of iron (rusting) occurs in presence of water
and oxygen (air).
At one spot of an iron object, oxidation occurs and this is thus the
anode.
Anode
Electrons from the anode move through the metal and go
another spot on the metal and reduce 
in
presence of
ions.(
gets
dissolved in water forming 
and which
releases ions,
).
This spot where reduction takes place is the cathode.
Cathode 
Net 
[1]
ions
move through water on the surface of the iron object. If water present in
saline, it will help more in carrying the current in the electrochemical cell
formed. Fe2+ ions are further oxidised by atomospheric O2
to Fe3+ (as 
)
and comes out as rust in the form of a hydrated iron (III) oxide represented as
ions
produced in this reaction help in further rusting. [1]
(b) Molar conductance at concentration
Conductivity
(specific conductance) 
Then,
is
practically expressed in the unit of 
(conductivity)
= conductance x cell constant. [1]
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