The correct answer is option 'B', German silver.

Explanation:
German silver is an alloy that does not contain any silver. It is primarily composed of copper, zinc, and nickel. Here is a detailed explanation of each option:

a) Horn silver:
Horn silver, also known as silver chloride (AgCl), is a chemical compound that contains silver. It is a naturally occurring mineral that is often found in the form of colorless or white crystals. It is used in various applications such as photography, silver plating, and chemical synthesis.

b) German silver:
German silver, also known as nickel silver, is an alloy that does not contain any silver. It is primarily composed of copper, zinc, and nickel. Despite its name, German silver does not contain any silver. It is called German silver because it was originally developed in Germany as a cheaper alternative to sterling silver.

c) Ruby silver:
Ruby silver is not a commonly known term. However, if it refers to a specific compound or material, it would likely contain silver. Without further information, it is difficult to determine whether it contains silver or not.

d) Lunar caustic:
Lunar caustic, also known as silver nitrate (AgNO3), is a chemical compound that contains silver. It is a highly versatile compound used in various applications such as photography, medicine, and chemical synthesis. It is known for its corrosive properties and is often used as a cauterizing agent.

In summary, German silver is the only option among the given choices that does not contain silver. It is an alloy made of copper, zinc, and nickel. The other options, horn silver, ruby silver (if it exists), and lunar caustic, all contain silver in different chemical forms.