compare the results of heating water with table salt and hydrochloric acid with magnesium metal?

Answer 1

Salt water will have very little effect on magnesium metal. Even in the hot solution you will see only a few bubbles on the surface of the Mg metal. This is because there will be very few H+ ions present. Compare that with HCl, where you get a vigorous reaction due to the presence of a lot of H+ ions:

Mg + 2HCl ----> MgCl2 + H2