Q. 25.0( 9 Votes )
Which of the foll A. Hardening of cement
B. Freezing of ice cream
C. Opening a door
D. Melting of chocolate
When powdered cement is mixed with water, it hardens. This is because of formation of new structures, called crystals, which after a fixed time get attached to each other, providing strength and hardening the cement. Therefore, as hardening of cement includes a change in its physical state and it’s chemical properties, it cannot be reversed back.
● A frozen ice- cream melts when kept in a warm room, a door can be closed after it is opened and a melted chocolate can be frozen back when kept in a refrigerator.
● As all these changes can be undone, or the items used can be brought back to their original state, they are said to be reversed.
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