The correct option for the question is **D. co-ordinate bond**. ### Explanation of the Correct Answer 1. **Understanding Ammonia and Hydrogen Ion**: - Ammonia (NH₃) is a molecule that has a nitrogen atom bonded to three hydrogen atoms. The nitrogen atom has a lone pair of electrons, which means it has two electrons that are not involved in bonding. - The hydrogen ion (H⁺) is simply a proton, which has no electrons. It is positively charged and can accept electrons. 2. **Formation of Ammonium Ion**: - When ammonia (NH₃) encounters a hydrogen ion (H⁺), the nitrogen atom donates its lone pair of electrons to the hydrogen ion. This process results in the formation of the ammonium ion (NH₄⁺). - The bond formed in this process is known as a **co-ordinate bond** (or dative bond). In a co-ordinate bond, one atom provides both electrons for the bond, while the other atom provides none. 3. **Characteristics of Co-ordinate Bonds**: - In a co-ordinate bond, the atom that donates the electron pair is called the donor (in this case, nitrogen in ammonia), and the atom that accepts the electron pair is called the acceptor (the hydrogen ion). - The resulting bond is similar to a covalent bond, but the key difference is in the origin of the shared electrons. ### Why the Other Options are Incorrect - **A. Ionic Bond**: - An ionic bond is formed when one atom donates an electron to another atom, resulting in the formation of charged ions that attract each other due to electrostatic forces. In this case, there are no ions formed; instead, a neutral ammonium ion is created through the sharing of electrons. - **B. Electrovalent Bond**: - The term "electrovalent bond" is synonymous with ionic bond. Since the bond between ammonia and the hydrogen ion does not involve the transfer of electrons to form charged species, this option is also incorrect. - **C. Covalent Bond**: - A covalent bond involves the sharing of electrons between two atoms, where each atom contributes at least one electron to the bond. While the bond in the ammonium ion does involve sharing, it is specifically a co-ordinate bond because the nitrogen atom provides both electrons for the bond with the hydrogen ion. ### Summary of Key Points - The bond formed between ammonia (NH₃) and hydrogen ion (H⁺) to create ammonium ion (NH₄⁺) is a **co-ordinate bond**. - In a co-ordinate bond, one atom (the donor) provides both electrons for the bond, while the other atom (the acceptor) does not contribute any electrons. - This process is distinct from ionic and covalent bonding, which involve different mechanisms of electron transfer and sharing. - Understanding the nature of bonds is crucial for grasping concepts in chemistry, especially in acid-base reactions and coordination chemistry. ### Revision Summary - Ammonia and hydrogen ion form ammonium ion through a **co-ordinate bond**. - A co-ordinate bond involves one atom donating both electrons to the bond. - Ionic and covalent bonds differ in electron transfer and sharing mechanisms. - Recognizing the type of bond is essential for understanding chemical reactions and molecular structures.