The correct option is **A. a compound which has no water of crystallization**. ### Detailed Explanation: 1. **Definition of Anhydride**: - An anhydride is a chemical compound that is derived from another compound by the removal of water (H₂O). The term "anhydride" literally means "without water." In the context of chemistry, anhydrides are often discussed in relation to acids and bases. For example, sulfuric acid (H₂SO₄) can lose a water molecule to form sulfur trioxide (SO₃), which is an anhydride of sulfuric acid. 2. **Understanding Water of Crystallization**: - Many salts and compounds can incorporate water molecules into their crystalline structure, which are referred to as water of crystallization. When these compounds are heated or treated in a way that removes this water, they become anhydrous (without water). For example, copper(II) sulfate (CuSO₄) can exist as a hydrated form (CuSO₄·5H₂O) and as an anhydrous form (CuSO₄) when the water is removed. 3. **Why Option A is Correct**: - Option A correctly identifies an anhydride as a compound that lacks water of crystallization. This definition aligns with the fundamental concept of anhydrides in chemistry, making it the most accurate choice. ### Analysis of Other Options: - **Option B: an oxide whose solution in water has a pH greater than 7**: - This option describes a basic oxide, which is not the definition of an anhydride. While some anhydrides can form basic solutions when dissolved in water (like sodium oxide forming sodium hydroxide), not all anhydrides fit this description. Therefore, this option is too specific and does not encompass the broader definition of anhydrides. - **Option C: an oxide whose solution in water has a pH less than 7**: - This option describes an acidic oxide, which is also not the definition of an anhydride. Similar to option B, while some anhydrides can produce acidic solutions (like carbon dioxide forming carbonic acid), this does not define anhydrides in general. Thus, this option is also incorrect. - **Option D: an oxide that has hydrogen atoms**: - This option is misleading. Anhydrides are not defined by the presence of hydrogen atoms. While some anhydrides may contain hydrogen (like acetic anhydride), the presence of hydrogen is not a requirement for a compound to be classified as an anhydride. Therefore, this option is incorrect. ### Summary of Key Points: - An anhydride is a compound that lacks water of crystallization. - Anhydrides can be derived from acids or bases by the removal of water. - Basic and acidic oxides are not synonymous with anhydrides. - The presence of hydrogen atoms is not a defining characteristic of anhydrides. This thorough understanding of anhydrides will help you recognize their significance in various chemical reactions and their role in forming acids and bases.