How do you find the oxidation number for a metal in a compound?

An experimental procedure requires a 10 ml of acid to be dissolved

If a solution had a ph of 7 what is the solution

Alidded glass container is filled with a colored gas. after a period of time, it is observed that the gas is uniformly spread throughout the box and that the movement has slowed considerably. next, a warm iron plate is carefully placed under the box. why is there resumed movement of the gas in the container?