State your observations when:
(A) Dilute hydrochloric acid is added to lead nitrate solution and the mixture is heated.
(B) Barium chloride solution is mixed with sodium sulphate solution.
(C) Concentrated sulphuric acid is added to sugar crystals.
(D) Dilute hydrochloric acid is added to copper carbonate.
(E) Dilute hydrochloric acid is added to sodium thiosulphate.

Hint: To solve the given question, we should have knowledge about dilute Hydrochloric acid, Sulphuric acid and Barium chloride solution like solvents.Sulphuric acid is also a mineral acid consisting of elements like Sulphur, Oxygen and Hydrogen. It is also known as Oil of Vitriol. It is colourless, odourless and viscous liquid soluble with water at any concentration.
Dilute hydrochloric acid converts solutes into soluble chloride salt. It is a hazardous liquid which is corrosive in nature and can cause severe skin damage when brought in contact. Barium chloride solution is an inorganic compound. It is white in colour, toxic in nature and is hygroscopic.

Complete answer:
-When we add dilute Hydrochloric acid i.e. $ HCl $ into lead nitrate solution, i.e. $ Pb(NO_3)_2 $ , the process leads to the formation of white precipitate of lead chloride along with nitric acid.
-When the barium chloride solution $ BaCl_2 $ reacts with sodium sulphate solution, $ Na_2SO_4 $ , a double displacement reaction takes place resulting in the formation of white coloured precipitate of Barium sulphate along with sodium chloride.
-When concentrated sulphuric acid is added to sugar hydrogen and oxygen from sugar molecules leaving behind black carbon. This phenomenon is known as charring of sugar.
-When dilute hydrochloric acid, $ HCl $ is added to copper carbonate, $ CuCO_3 $ ,it goes into the decomposition process to form copper chloride, $ CuCl_2 $ along with water and carbon dioxide gas.
-When sodium thiosulphate, i.e. $ Na_2S_2O_3 $ reacts with dilute hydrochloric acid, the colourless solution turns opaque due to the formation of colloidal sulphur left behind along with sulphur dioxide gas and water.

Note:
Sodium thiosulphate, $ Na_2S_2O_3 $ has been regarded as one of the most effective and safe medicines needed in the health system by the World Health Organization.