(a) Which of the following metals cannot be extracted by the smelting process ?
`Al, Zn, Fe` and `Pb`.
(b) Graphide is used as anode but not diamond. Give reason.
( c) Give a method for separation of nickel from cobalt ?

Explanation

(a) Aluminium cannot be extracted by the smelting process because :
(i) `Al`is highly electropositive element and has strong affinity for oxygen. Hence, `Al_(2) O_(3)` is a very stable compound and is not reduced by carbon.
(ii) `Al_(2) O_(3)` on heating with carbon forms aluminium carbide `(Al_(4) C_(3))`
`2 Al_(2) O_(3) + 9C rarr Al_(4) C_(3) + 6 CO`
(b) Graphite is a good conductor of electricity due to presnece of free eletrons within its layers, which help in conductor of electricity . Hence, graphite can be used as an anode. Whereas, diamond is bad conductor of electricity due to absence of free electrons in its structure. Hence, diamond cannot be used as an anode.
( c) Nickel `(Ni)` can be separated from cobalt `(Co)` by Mond's process. `CO` is passed over a heated mixture of `Ni` and `Co` at `330-350 K`, when `Ni` forms volatile `Ni(CO)_(4)` but `Co` does not. The volatile `Ni(CO)_(4)` is separated and then heated at `450-470 K` to get pure `Ni`
` underset("Impure nickel") (Ni) + 4CO overset (330 - 350 K)rarr underset("Nickel tetracarbonyl") (No(CO)_(4)) overset(450-470 K)rarr underset("Pure nickel") (Ni) + 4CO`.