egg floats in water because density of egg is less than the density of salt water. while the same egg will sink in water because the density of water is less than the density of egg 

i hope it helps.................... 
1 5 1
An egg doesn't float in fresh water but since salt water is denser than fresh water, it has a better chance of floating in the salt water. The greater buoyant force allows the egg to float in the salt water, if salty enough.