Question

Which of the following is the least reactive metal?
A. Aluminium
B. Iron
C. Platinum
D. Calcium

Answer 1

Reactivity of metals is briefly arranged according to their reactive nature in the reactivity series of metals. In this series metals are arranged from top to bottom being most reactive metals on top and least reactive metals which are noble metals at the bottom.

Complete step-by-step answer: Let us look at the reactivity of all the metals one by one. First we have aluminium. Aluminium is indeed a reactive metal. It has three valence electrons in its last shell. It comes eighth from the top in reactivity series. It reacts with oxygen in air to form a thin transparent inert layer of aluminium oxide $(A{l_2}{O_3})$ . This layer prevents corrosion on the surface of aluminium. But by removing this inert layer the reactive nature of aluminium can be utilized to form various compounds.
As we are well aware about the compounds of iron and its uses it is obvious iron is a reactive metal. It comes eleventh from the top in reactivity series. Iron reacts with oxygen in air to form $F{e_2}{O_3}$ which is commonly known as rust. It dissolves in almost most acids. Iron also reacts with hot water and steam to produce hydrogen gas.
Calcium is also a reactive element. It has two electrons in its valence shell. It comes sixth from the top in reactivity series. On coming in contact with water it forms calcium hydroxide $(Ca{(OH)_2})$ .
Platinum is known to be one amongst the noble metals. It is so because of its inert nature. It is placed at the bottom in the reactivity series. It does not undergo any oxidation even under high temperatures. Hence we can say platinum is the least reactive metal among the given metals.

So option C is the correct answer.

Note: As platinum is of the least reactive metal, it is found as native platinum which is chemically uncombined. Platinum does not dissolve in acids nor it is affected by any action of any mineral but it dissolves in aqua regia.