Why is it dangerous to keep a sodium metal in your pocket?
Because it might give you a nasty surprise.........
Sodium reacts with water according to the following reaction.....
Were you to handle a chunk of sodium or potassium metal the metal would react with the water on your hands and form an hydroxide salt. Base burns are usually much worse than acid burns in that the soapiness of the former often means you have done some damage to your skin before you realize it hurts; an acid burn stings immediately.
Anyway, when you handle alkali metals typically you keep the metal chunks in a tin filled with paraffin oil; you don't want sticky oil in your pockets.
When you use sodium metal in the lab, you take care to contain ALL the sodium residues and tissues and knives used for cutting the metal, and douse them all with ethyl alcohol; such a solvent usually safely degrades the sodium. You do not do this to destroy residues of potassium, which is a much more reactive and hazardous metal.