Explanation:
Salinity is the measure of the concentration of dissolved salts in water. The Dead Sea is known for its extremely high salinity, making it one of the saltiest bodies of water in the world. Here's a detailed explanation:

Dead Sea:
- The Dead Sea is located between Jordan to the east and Israel and Palestine to the west.
- It is a saltwater lake that is bordered by Jordan to the east and Israel and Palestine to the west.
- The Dead Sea has a salinity of around 34%, which is almost ten times saltier than the world's oceans.
- Due to its high salinity, no fish or other aquatic organisms can survive in the Dead Sea.
- The salt and minerals from the Dead Sea are used in various industries, including cosmetics, agriculture, and medicine.

Red Sea:
- The Red Sea is located between Africa and Asia.
- It is a saltwater inlet of the Indian Ocean.
- The Red Sea has a salinity of 40 parts per thousand (ppt), which is higher than the world's oceans.
- The high salinity of the Red Sea is due to its location and the hot and dry climate in the region.

Black Sea:
- The Black Sea is located between Southeast Europe and Western Asia.
- It is a saltwater sea that is connected to the Mediterranean Sea.
- The Black Sea has a salinity of around 18 ppt, which is lower than the world's oceans.
- The low salinity of the Black Sea is due to the large amount of freshwater that flows into it from rivers.

Mediterranean Sea:
- The Mediterranean Sea is located between Europe, Africa, and Asia.
- It is a saltwater sea that is connected to the Atlantic Ocean.
- The Mediterranean Sea has a salinity of around 38 ppt, which is higher than the world's oceans.
- The high salinity of the Mediterranean Sea is due to its location and the hot and dry climate in the region.

Therefore, the correct answer is that the Dead Sea has the highest average salinity amongst the following seas.