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प्रश्न
A bag of cement lying in the open gets wet due to rain during the night. The next day the sun shines brightly. Do you think the changes, which have occurred in the cement, could be reversed?
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उत्तर
In this case, the changes cannot be reversed. This is because the cement that hardens up after getting wet cannot be obtained back.
संबंधित प्रश्न
The gas we use in the kitchen is called liquefied petroleum gas (LPG). In the cylinder, it exists as a liquid. When it comes out from the cylinder it becomes a gas (Change − A), then it burns (Change − B). The following statements pertain to these changes. Choose the correct one.
Define precipitation reaction.
A solution of a substance ‘X’ is used for white washing write the reaction of the substance ‘X’ named in (a) above with water.
Define a photochemical reaction.
State the type of reactions for the following represent and balance the ones that are not balanced.
Cl2 + 2KBr → 2KCl + Br2
State the original colour of the following substance and colour of residue obtained after heating.
Ammonium dichromate
Give a balanced equation for the conversion of an ammonium salt to a basic gas.
Higher order Thinking question
A very hot glass on putting in cold water cracks. What does this change indicate?
Which of the following is not an “element + element → compound” type reaction?
Write some materials prepared by chemical changes.
