You can tell if your snail is dead by gently touching its foot. If it does not retract, it may be dead. Also, an unpleasant odor and a dried-up body are signs of a deceased snail.
Not necessarily as lots of snails float from time to time. Pick it up and touch the foot with your finger and see if it reacts.
The only way to tell if a snail is dead is to sniff the snail, if it gives off a strong, odorous scent, it is most likely dead.
It will stink like dead fish.
if it hasn't moved in a week it is probably dead
the amount of salt dissolved in the water
its shell drops off its body, or it lays upside-down on the bottom of the tank
Snails are hermaphrodites, so they are both male and female.
The density of a salt water solution compared against the densities of "pure" water and salt provides an approximate value of the ratio of water to salt in the mixture.
Salt is the solute. Water is the solvent. Salt water is the solution. This solution is sometimes called a saline solution.
Snails that do not move for a day are definitely not well. An easy way to tell is to pick it up and smell it, and if it smells rotten, then its dead or dieing. Don't inhale too deeply, as rotting snail smell is one of the most disgusting smells you can smell.
Snails stink horridly when they die. If you have the stomach, you can pick he/she up and get a little whiff. Trust me, you'll know then if he/she is dead or not.