Which of the following gold casting alloys are available?

Gold casting alloys are classified based on their gold content and the hardness properties they exhibit, which include various types that are suitable for different dental applications.

Medium alloy, categorized as "Type II," is known for its balanced properties that make it suitable for a variety of dental restorations, providing a good degree of strength and workability.

The hard alloy, or "Type III," is characterized by an increased strength, which is beneficial for restorations that require greater resistance to deformation. This makes it ideal for applications where durability is crucial, such as posterior crowns.

Extra hard alloy, labeled as "Type IV," is designed for high-strength applications, typically used in areas requiring maximum wear resistance, such as castings for bridges and other load-bearing structures.

Since each of these types of gold casting alloys serves specific functions and provides varying benefits depending on the requirements of the dental application, it is accurate to state that all of these alloys are available for use in practice. This diversity allows dental professionals to choose the appropriate alloy type based on the needs of the restoration they're performing.