Q19. What is crystallisation?
Q20. Why a wet iron pan often gets rusted if left in that state for some time?
Q21. Why does rusting takes place faster during rainy season?
Q22. What are physical properties?
Q23. What is a physical change?
Q24. What is called a chemical reaction?
Q25. Why a slice of an apple acquires a brown colour if it is not consumed immediately?
Q26. Write down the equation representing the process of rusting.
Q27. Why tearing of paper into pieces is a physical change?
Q28. What happens when magnesium oxide is dissolved in water?
Q29. Why is spoiling of food a chemical change?
Q30. How would you show that setting of curd is a chemical change?
Q31. Why explosion of fireworks is a chemical change?
Q32. Explain how painting of an iron gate prevents it from rusting.
Q33. Why is hacksaw blade’s color change on heating considered as a physical change?
Q34. Why do ships suffer a lot of damage from rusting in spite of being painted?