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.  

kepler used the data from tycho blahe (his mentor) to construct the laws of planetary motion.

the part of the wave he is travelling on is the crest