Which element has atoms that can form halide ions? (1) iodine (3) strontium (2) silver (4) xenon
The Correct Answer and Explanation is:
The correct answer is (1) iodine.
Halide ions are negatively charged ions formed when halogens (elements in Group 17 of the periodic table) gain one electron. Iodine is a halogen, and like other halogens (fluorine, chlorine, bromine, etc.), it readily gains an electron to form a halide ion. When iodine gains an electron, it forms an iodide ion (I−I^-I−).
Explanation:
- Iodine (I) is in Group 17, which is the halogen group. The halogens have seven valence electrons and tend to gain one electron to complete their octet, thus forming a negative ion (anion). When iodine gains one electron, it becomes I−I^-I−, the iodide ion.
- Silver (Ag) is a metal and typically forms positive ions, not halide ions. It usually forms a Ag+Ag^+Ag+ ion when it loses one electron, but it can combine with halogens (such as chlorine or iodine) to form silver halides (e.g., AgClAgClAgCl, AgIAgIAgI), where silver acts as the cation.
- Strontium (Sr) is an alkaline earth metal in Group 2, and it typically forms a Sr2+Sr^{2+}Sr2+ ion by losing two electrons, not a halide ion.
- Xenon (Xe) is a noble gas (Group 18) and generally does not form halide ions under normal conditions. Noble gases have a full octet of electrons and are chemically inert.
Thus, iodine is the only element in the list that can form halide ions like I−I^-I−.
