Science [3 Marks Question]

1. Boiling
2. Water in the kettle gets converted into vapour
3. Endothermic
4. Water vapour converted into liquid (condensation)

1. Physical change
2. Chemical change
3. Exothermic

• Boiling of water is a physical change:

• Boiling of egg is chemical change:

1. When sugar is dissolved in water it disappears. It we taste the solution, the sugar is still present in dissolved form.
2. If water is evaporated we get back the sugar.
3. So it is a physical and reversible change.

2. Burning of sugar:

1. Fire activates a chemical reaction between sugar and oxygen. The oxygen in the air reacts with the sugar as the chemical bonds broke.
2. Energy is released in the form of smoke.
3. So, burning a sugar is a chemical change.

1. First the ring in the iron blade of spade is heated.
2. Heating of the blade leads to its expansion and thus the ring gets bigger.
3. This happens because metals always expand on heating.
4. The metal blade is then fitted easily into the wooden handle.
5. After this, cold water is usually poured on the iron blade which leads to the contraction of the expanded iron blade.
6. The spade can also be left to cool down, undisturbed so that it is firmly fixed, (vu) The blade is attached firmly to the wooden handle of a spade in this process.

1. When we eat, our mouth physically break down food into small pieces.
2. Mechanical digestion occurs in the mouth, stomach and small intestine.
3. Food is chemically changed in digestion when new, smaller substances are formed.
4. Moreover, we will never be able to get back the raw material in the same form as it was before.
5. Digestion of food is a permanent change which is irreversible.