Which of the following is an ore of silver? 

Argentite

The correct answer is option 3. Argentite.

Argentite is a silver sulfide mineral with the chemical formula Ag2S. It is an important ore of silver and is often found associated with other silver minerals. The mineral has a dark gray to black color and a metallic luster. Argentite crystallizes in the cubic system, and its hardness on the Mohs scale is relatively low, ranging from 2.5 to 3.5.

When argentite is exposed to certain chemical processes, it can be converted to metallic silver, making it a valuable source of silver extraction. The extraction of silver from argentite involves processes such as smelting and various chemical reactions to obtain pure silver metal. Overall, argentite plays a significant role in the production of silver, a precious metal with various industrial and ornamental uses.