Question

state any two observation in which activity suggestion is occurrence of a chemical reaction​

Answer 1

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When a chemical reaction takes place any of these changes can be observed:

★ Change in color.

★ Change in state.

★ Evolution of gas.

★ Change in temperature.

★ Formation of precipitate.

Example:

★ When lead nitrate and potassium iodide reacts, a yellow precipitate i.e. lead iodide is formed.

★ When sodium reacts with water, sodium hydroxide is formed along with the evolution of hydrogen gas.

★ When green crystals of  iron oxide is heated, a successive color change is observed from green to colorless to reddish brown along with sulphur dioxide and sulphur trioxide.

★ When quicklime is mixed with water, its forms slaked lime and heat is evoluted and hence there is change in temperature.