On adding dilute hydrochloric acid to copper oxide powder,the solution formed is blue-green. Predict the new compound formed which imparts a blue-green colour to the solution.

Write true or false for the following statement: On heating the crystals of ferrous sulphate,the colour changes from green to grey.

State three applications of a decomposition reaction.

In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate,a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available,which of the following can be used in place of lead nitrate?

Give the characteristic tests for the following gases:
$(a)$ $O_2$
$(b)$ $H_2$

The substances which get oxidised easily can be kept for longer duration by: