Step 1: Meaning of salinity.
Salinity tells us how much salt is dissolved in a body of water. More dissolved salt means higher salinity.
Step 2: What raises salinity.
When water gets a lot of heat and evaporates fast, but very little fresh water flows in, the salt left behind keeps building up. Closed water bodies show this best.
Step 3: Look at the Dead Sea.
The Dead Sea lies between Jordan and Israel. It sits in a hot, dry area and has almost no outlet. Water leaves it mainly by evaporation, so salt collects there.
Step 4: Compare the others.
The Black Sea, Red Sea, and Mediterranean Sea are salty too, but they are open to oceans and get more fresh water, so their salt level stays much lower.
Step 5: The result.
Because of heavy evaporation and no real outflow, the Dead Sea holds far more salt than any of the others. You can even float on it easily.
Step 6: Conclusion.
So the highest salinity belongs to the Dead Sea.
Answer: The Dead Sea