What is Na2S?

It is a Ionic bond between Sodium Ions and Sulfide Ions. The formula name is Sodium Sulfide. Na = sodium S = sulfur Sodium Sulfide?
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What happens to water when add indicator?

water is pretty neutral in terms of the pH scale, so nothing should happen unless you have poisoned water .It'll turn green if you used universal indicator(pH7), after you add (MORE)

What happens to the indicator when a base is added?

There are a huge range of indicators that can be used in chemistry, but I presume you'll be using the basic 'universal indicator' here. A base will turn this indicator (depend (MORE)