i know that metal placed in more acidic solution will produce rust faster.but why metal placed near the sea shore will easily have rust?the wind with moisture which contains salt solution,right?

however ,i have a problem.When i put the metal in the test tube with sodium chloride solution,it rust slower than the one i put in distilled water with air,why

Oxygen is one of the ingredients of rusting. Salt + oxygen + H2O should increase the rate of rusting.