(a) (i) Describle a method for refining nickel.
(ii) Why group 18 elements are called inert gases ? Write the general electronic configuration of group 18 elements.
(b) (i) Give the uses of helium.
(ii) Ni(II) compounds are more stable than Pt(II) compound.Give reason.

Explanation

(i) The impure nickel is heated in a stream of carbon monoxide at around 350 k. The nickel reacts with the co to from higly volatic nickel tetracarbony. The solid impurities are left behind.
`Ni(s) +4 co (g) to Ni (co)_(4) (g)`
On heating the nickel tetracarbonyl around 460 k the complex decomposes to give pure metal .
(ii) the elements of group -18 have complety filled s and p orbital hence they are more stable and have least reactivity .Therefore group -18 elements are called inert gases.
(b) (i) Uses of helium
1. Helium and oxygen mixture is used by divers in place of air oxygen mixture . This prevents the painful dangerous condition called bends.
2. Helium is used to provide inert atmosphere in electric welding of metals
3. Helium has lowest boiling point hence used in cryogenic .
4. If is much less denser than air and hence used for filling air ballons.
(ii) The ionisation enthalpy values can be used to predic the themodymic stability of their compound .
For Nickel .` Le_(1) + LE_(2) = 737 + 1753`
Since the energy required to from `Ni^(2+)` is less than that `Pr^(2+)` Ni (II) compounds are thermodynamically more stable thant P (ii) compounds.