b. Polar covalent bonds. The polar N-H bonds hold the NH3 molecules together. They are intramolecular forces of attraction within a molecule.
All the other options are wrong. They are intermolecular forces — the attractive forces between different molecules.
[tex]\boxed{{\text{c}}{\text{. Hydrogen bonding}}}[/tex] holds the molecules together in a sample of ammonia.
Further Explanation:
Intermolecular forces exist between the molecules. Both attractive and repulsive forces are involved in it. These forces are capable to hold the molecules together in any substance.
The various types of intermolecular forces are as follows:
1. Dipole-dipole attraction
This type of forces exists when the charged part of one polar molecule interacts with the oppositely charged part of another polar molecule. The one end of polar molecule acquires partially positive charge while the other end develops partially negative charge.
2. Ion-dipole forces:
As is evident from its name, this force arises between an ion and a neutral molecule that consists of a dipole. This type of force is significant for solutions of ionic compounds in polar solvents.
3. Ion-induced dipole forces:
This force arises between an ion and a non-polar molecule. The ion induces a dipole in the non-polar molecule. As a result, a dipole is induced in the non-polar molecule.
4. Dispersion forces:
These forces exist between atoms and molecules. The forces that occur in [tex]{{\text{H}}_2}[/tex] molecule is a dispersion force.
5. Hydrogen bonding:
The force that takes place between a more electronegative atom and hydrogen is known as hydrogen bonding. N, O, F are highly electronegative in nature and therefore capable to form hydrogen bonds with hydrogen.
Polar covalent bond:
It is a type of bond where the electronegativity of the bonded atoms is different but the bond is formed by mutual sharing of electrons. For example, HCl has a polar covalent bond due to electronegativity difference between H and Cl.
In [tex]{\text{N}}{{\text{H}}_{\text{3}}}[/tex], nitrogen is more electronegative than hydrogen. Since hydrogen bonding exist between hydrogen and an electronegative element, hydrogen bonds are responsible to hold the molecules together in ammonia.(For structure, refer to the attached image).
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Answer details:
Grade: Senior School
Subject: Chemistry
Chapter: Ionic and covalent bonding
Keywords: ammonia, NH3, hydrogen bonding, dispersion forces, dipole-dipole, ion-dipole, ion-induced dipole.
