Final answer:
Yes, it is true that people can float in the Dead Sea and the Great Salt Lake due to their high salt concentrations. However, it is not impossible to sink in the Red Sea and the Mediterranean Sea as the salt content in these seas is not as high.
Step-by-step explanation:
Yes, it is true that people float in the Dead Sea due to its high salt concentration. The water in the Dead Sea contains a sodium concentration that is 10 times higher than that of seawater, making it extremely buoyant. This high salt concentration makes it impossible for a person to sink in the Dead Sea without added weight.
Similarly, the Great Salt Lake in Utah also has a high salt concentration which allows people to float on its surface. The salt content in the Great Salt Lake is even higher than that of the Dead Sea.
As for the Red Sea and the Mediterranean Sea, while they have higher salt concentrations than regular ocean water, they do not have the same level of salinity as the Dead Sea or the Great Salt Lake. Therefore, it is not as easy to float on the surface of these seas without any added weight.