Question

Which of the following non-metal is a liquid?
A. carbon
B. sulphur
C. bromine
D. iodine

Answer 1

Hint: The answer of this question is red-brown liquid. We should know that the elemental form of this is very reactive and thus does not occur free in nature. It is the third lightest element in its fellow group.

Step by step answer:
To answer this question, we should know that the attractive forces between the molecules of these elements increase from top to bottom of the Group. We should know that intermolecular forces are the attractive forces between molecules without which all substances would be gases. The molecules of each substance attract each other through dispersion (London) intermolecular forces. Whether a substance is a solid, liquid, or gas depends on the balance between the kinetic energies of the molecules and their intermolecular attractions.

Now, we will look at each option to check which non-metal is liquid.

First option is carbon; we know that carbon exists in different forms. These different forms are known as allotropes. So, carbon exists from diamond to coal. This non-metal is solid.

Second option is sulphur. We should know that sulphur does not form strong S=S double bonds hence it exists as $S_8$, which is held together by strong covalent bonds and exists as a polyatomic molecule, in which intermolecular forces are strong, so it exists as a solid.

Last two options, bromine and iodine are from the halogen family. We should know that Bromine is a liquid because electrons are well apart from the nuclei so they are easily distorted. Intermediate intermolecular forces exist and thus it is in liquid state. Iodine is a solid because as its atom size is larger, the electrons are so far that the electron cloud gets very easily distorted. It has very strong intermolecular London forces which make it a solid.
So, from this above discussion, we came to know the correct answer of our question, which is bromine, option C. We should know that bromine is the only non-metal that is liquid at room temperature.

Note: One important property that we should discuss in the halogen family is that of ionization energy. First ionisation energy is the complete removal of an electron from the gaseous halogen atoms in which fluorine has the highest ionisation energy and iodine the lowest. This can be explained by variation of size, as the size increases it takes less energy to remove an electron.