The atoms of two elements are identical as long as you are not speaking of isotopes or ions.

 

No water cannot stay liquid below zero degree at normal conditions. At zero degree water and ice are in a equilibrium state. Water can be found below zero degree only if you vary the pressure or add impurity ( a non volatile substance to be precise) to it. Eg- In Northern countries salt is sprayed on roads so as to prevent the formation of ice and lowering the freezing point.

The Mathematical approach to this would be-   reduction in freezing point= K(cryoscopic constant) * molality of non volative substance ( Salt in the above example).

 

Add the acidic product to baking soda or washing soda. You will get a residue of white NaCl.

Also acidic foods are normally sour in taste. ( A little intake of weak acids like acetic acid and citric acid wont hurt as we intake them almost daily).