Olympiad Test: Changes Around Us - Class 6 MCQ

The changes that can be reversed in this scenario are melting of the wax (i) and the solidification of the melted wax (iv). Melting and solidification are reversible changes as they involve the transition of matter between solid and liquid states. When the candle is cooled, the melted wax solidifies back into a solid form. Interestingly, this property of wax is commonly utilized in making candles.

Metal X is iron which reacts with blue coloured solution of copper sulphate and forms a new substance (green coloured solution of iron sulphate). It is an irreversible and chemical change.

A change in which a substance undergoes a change in its physical properties is called a physical change. It is generally reversible and in such a change, no new substance is formed. For example, boiling of water, dissolving of salt in water, melting of an ice cube. A change in which one or more new substances are formed by means of a chemical reaction is called a chemical change. It is generally irreversible. For example, setting of milk into curd, making idlis from batter, rusting nf iron eookina of food. etc.

n figure I, water evaporates from the sugar solution and sugar crystals are left behind, so it is a physical change. In figure II, when sugar is heated, it turns black due to the formation of a new substance and this change cannot be reversed. Therefore, it is a chemical change.