Which acid is dangerous between vinegar, pure water, lemon juice and milk?

Explanation:

Oftentimes when people hear that something has a low or high pH, they worry that it is dangerous. But this is not the case, pH alone cannot tell you if a substance is dangerous or not. Anyway, bases are typically considered more dangerous than acids! But what is pH? A substances pH is simply the concentration of hydrogen ions (H+) of the material when in solution (usually water). It is a numeric (logarithmic) scale used to specify how acidic or basic an aqueous solution is and an aqueous solution is just a solution where water is the solvent.  

coil wire, increase current, put iron inside the coil