If you try to cook an egg boiling water while camping at elevation pf 0.5 km in the mountainyou will find that it takes longer than it does at home .Explain why?

At higher elevations, the atmospheric pressure is less. As you reduce the pressure, the temperature at which water boils is reduced. So, it will NOT take longer to boil, but will take shorter. It doesn't have to reach 212ºF at elevations, so it will boil at a lower temperature, which should take less time, unless, of course, you have a lot of wind or something else affecting the time to reach this lower temperature. In fact, the boiling point for water at 500 m above sea level is approximately 209ºF compared to 212ºF at home, depending on where home is.