81. When iron is placed in moist air, a reddish brown layer of hydrated iron (III) oxide (Fe2O3) accumulates on its surface. This reddish brown layer is called:
82. Consider the following elements.
1. Cobalt
2. Phosphorus
3. Zinc
Which of the above elements are required for maintaining the healthy human body?
1. Cobalt
2. Phosphorus
3. Zinc
Which of the above elements are required for maintaining the healthy human body?
83. Which one of the following materials is very hard and very ductile?
84. Match List I with List II.
List-I (Mineral)
List-II (Industries in which largely used)
a. Limestone
1. Cement
b. Copper
2. Electrical goods
c. Bauxite
3. Manufacture of aeroplanes
d. Manganese
4. Steel
| List-I (Mineral) | List-II (Industries in which largely used) |
| a. Limestone | 1. Cement |
| b. Copper | 2. Electrical goods |
| c. Bauxite | 3. Manufacture of aeroplanes |
| d. Manganese | 4. Steel |
85. The corrosion of . . . . . . . . is a serious problem-
86. When sodium sulphate solution is mixed with barium chloride solution,
87. Sodium is a reactive metal, which if kept open reacts with . . . . . . . . explode and catch fire.
88. Bronze is an alloy of . . . . . . . .
89. Which of the following metals gives yellow colour to flame when ignited?
90. Which of the following is flexible and soft?
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