Question

Mercury is a liquid metal because,
A.It has a completely filled s-orbital
B.It has a small atomic size
C.It has a completely filled d-orbital that prevents d-d overlapping of orbitals.
D.It has a completely filled d-orbital that cause d-d overlapping

Answer 1

Hint: Mercury is the only metal which is known to exist in liquid state. This unique property of mercury is due to its unique electronic configuration. Mercury has a symbol Hg and it belongs to the d-block in the periodic table.

Complete step by step answer:
Mercury is a shiny, silvery liquid. Its atomic number is $80$ . It belongs to the sixth period and twelfth group in the periodic table. The electrons in mercury are tightly bound to the nucleus compared to other metals. The electronic configuration of mercury is,
${\left( {1s} \right)^2}{\left( {2s} \right)^2}{\left( {2p} \right)^6}{\left( {3s} \right)^2}{\left( {3p} \right)^6}{\left( {4s} \right)^2}{\left( {3d} \right)^{10}}{\left( {4p} \right)^6}{\left( {5s} \right)^2}{\left( {4d} \right)^{10}}{\left( {5p} \right)^6}{\left( {6s} \right)^2}{\left( {4f} \right)^{14}}{\left( {5d} \right)^{10}}$
The outermost orbital of mercury is $6s$. It has a completely filled $6s$ orbital. The screening power of f-orbitals is very poor. Hence screening of $6s$ by inner orbitals is not much effective. $6s$ is strongly bound to the nucleus. It stabilizes the $6s$ orbital. Therefore it is difficult to remove the outer electrons unlike in other metals. Hence mercury cannot easily form bonds with other elements. This is the reason why mercury exists in a liquid state. It almost behaves like a noble gas because of the completely filled $6s$ orbital.
In brief, Mercury is a liquid metal because it has a completely filled s-orbital.
The correct answer to the question is option A.

Note:
Other metals can easily share their valence electrons and form bonds with other elements. Mercury is used in thermometers because of the unique property of being in liquid state at room temperature and high value of coefficient of expansion.