The following method of purification,where metal is converted to its volatile compound that gives pure metal is upon the decomposition :

a.  Heating with a stream of carbon monoxide.

b.  Heating with iodine.

c.  Liquation

d.  Distillation

Choose the correct option :

1. (a, b)
2. (b, c)
3. (c, d)
4. (a, d)

HINT: Mond's process and van Arkel method.
Vapour phase refining method includes.

(i) Heating of metal with stream of CO: 
Mond process for refining of Nickel is based on the principle that nickel is heated in the presence of carbon monoxide to form nickel tetracarbonyl, which is a volatile complex.
Then, the obtained nickel tetracarbonyl is decomposed by subjecting it to a higher temperature (450 - 470 K) to obtain pure nickel metal.
Ni+ 4CO Ni CO4 450-470 K Ni+ 4CO Mond's process
(ii) Heating with iodine:
In this method oxygen and nitrogen, present as impurity are removed by heating metal in an evacuated vessel with iodine.
The metal iodide volatize and it is decomposed on a tungsten filament, heated to about 1800K. The pure metal is deposited on the filament.
Zr+ 2 I2  870 K   ZrI4  2075 K    Zr + 2 I2 van Arkel method