Question

What is the Mohs hardness scale and how is it useful for identifying minerals?

Answer 1

Hint : You should have basic knowledge of Mohs scale of mineral hardness and then according to the malleable and ductile nature of metals you can think of the answer. And softness is nothing but the ability of a substance to get easily mould, cut, compress or fold.

Complete Step By Step Answer:
The softness of a metal refers to the ability of a metal material to deform easily through the intrusion of a hard object. As asked in question which is the softest metal among platinum, silver, iron and aluminium. To solve this question, we have to define Mohs scale of mineral hardness. The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. You should remember some general data that helps in solving many questions related hardness and softness of metal.
Mohs scale is a list of ten minerals. Each one has its own conventional degree of hardness and is one point harder than the next one. Here it is the scale:

MOHS SCALE

Hardness| Minerals| Examples
1| Talc| Graphite
2| Gypsum| Halite, Chlorite, Mica.
3| Calcite| Biotite, Gold, Silver
4| Flurit| Dolomite, Blende.
5| Apatite| Hematite, Lapis.
6| Orthoclase| Opal, Rutile.
7| Quartz| Garnet, Tourmaline.
8| Topaz| Beryl, Aquamarine.
9| Corundum|
10| Diamond|

But usually for these kinds of measurements precise, expensive and usually not mobile equipment is necessary. Besides it's not necessarily to know the precise hardness value to define a mineral. This makes instrumental measurement impossible and needles in field research. That's why the Mohs scale is so useful.

Note :
Note that the caesium is the softest metal with the Mohs hardness of $0.2.$ Always remember, the hardness of gold, silver, aluminium, zinc, lanthanum, cerium, jet is in between $2.5-3$ and that of platinum is $3.5$ (according to Mohs hardness).