Answer:
1. Insoluble yellow solid sulfur forms and gets deposited at the bottom. to setup the experiment draw a cross on a white paper and place beaker on top of it. take known volumes of sodium thiosulfate and hydrochloric acid in a beaker and mix it. At the same time start stop watch. measure time taken for the cross to disappear.
2. Sodium chloride, sulfurdioxide and water
3. increase concentration of acid