:X Express the group number as an integer:
The Correct Answer and Explanation is:
Correct Answer: 16
Explanation
The notation “:X” typically refers to a chemical element’s symbol, with the colon suggesting a relationship such as electron configuration or molecular structure. To determine the group number of an element represented by “X”, context is key. In most chemistry problems involving group numbers, we analyze the electron configuration or Lewis structure to determine the number of valence electrons, which directly corresponds to the group number in the periodic table for main-group elements (Groups 1–18).
For example, if “:X” refers to a chalcogen like oxygen (O), sulfur (S), or selenium (Se), these elements are all in Group 16. This group is characterized by having six valence electrons, making them reactive nonmetals capable of forming two covalent bonds to complete their octet. This is common in molecules like H₂O, SO₂, or H₂S, where X would represent oxygen or sulfur.
The group number is important because it tells us how many valence electrons an element has, which in turn determines how it bonds with other atoms. Group 16 elements tend to gain or share two electrons during bonding to achieve a stable electron configuration, often forming -2 anions in ionic compounds.
In a Lewis structure, an element from Group 16 typically has two bonding pairs and two lone pairs, reflecting its six valence electrons. This also impacts molecular geometry, with structures like bent or angular shapes (e.g., in water), due to the repulsion of lone pairs.
In summary, if “X” is from Group 16, it means the element has six valence electrons, commonly forms two bonds, and is involved in a variety of biologically and industrially important compounds. Therefore, the correct group number for X is 16.
