Water can push up harder than the soft, porous slice of bread can push down, so the bread slice floats. Squeezing bread into a wad changes its density. Stir vigorously to make the salt dissolve. Place the egg first in the glass of water without salt. Remove the egg and place it in the glass of saltwater.
Saltwater is denser than fresh water.
Denser water can push up on the egg harder than the egg can push down, so the egg floats. It may help to explain how density is like a suitcase. An empty suitcase is less dense than one that is packed for a vacation. Look at the list of questions you had when you started. Extensions Create water as salty as the oceans to understand saltwater's density and its comparison to fresh water.