Question

Which of the following has lowest melting point:
A.Cr
B.Fe
C.Ni
D.Cu

Answer 1

Hint:All the elements given in the question are d- block elements. These are those elements which correspond to the filling of the d- orbital of an atom. They generally have 1 to 10 electrons in the d- orbital of their penultimate shell and 1 or 2 electrons in the outermost shell. To answer this question, you must recall the factors on which the melting points of these elements vary. More are the number of unpaired electrons, more is the melting point.

Complete step by step answer:
The d- block elements are metals and show all general metallic properties, namely, malleability, ductility, thermal conductivity, good tensile strength and high electrical conductivity. Their properties are intermediate between those of the s- block elements and f- block elements and are thus known as transition metals. The d- block of the periodic table has 4 periods which correspond to the filling of the 3d, 4d, 5d and 6d orbitals.
The metals given in the above question belong to the 3d series.
Transition metals form both covalent as well as metallic bonds. The unpaired electrons in the partially filled d- orbitals of the transition metals form covalent bonds while the electrons present in the outermost s- orbital form metallic bonds. Due to these two types of bonding, they have high melting and boiling points. More the number of unpaired electrons in the d- orbital more is the additional bonding and thus, more is the melting point.
Of the given compounds, copper has the least number of unpaired electrons in the d- orbital and thus has the lowest melting point.

Thus, the correct answer is D.

Note:
Manganese has five unpaired electrons in the d- orbital and should have the highest melting point but it shows an exceptionally low melting point since all the electrons are less delocalized and have weaker interactions.