Science Most Imrtant Question-150
NCERT -10th (English Medium)
1. Write a balanced chemical equation with state symbols for the following reactions.
a. Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.
b. Sodium hydroxide solution (in water) reacts with hydrochloric acid solution (in water) to produce sodium chloride solution and water.
2. Explain the Oxidation and Reduction?
3. What is the Corrosion?
4. Explain the Double Displacement Reaction and Decomposition Reaction with example?
5. Write the balanced chemical equation for the following and identify the type of reaction in each case.
a. Potassium bromide(aq) + Barium iodide(aq) → Potassium iodide(aq) + Barium bromide(s)
b. Zinc carbonate(s) → Zinc oxide(s) + Carbon dioxide(g)
c. Hydrogen(g) + Chlorine(g) → Hydrogen chloride(g)
d. Magnesium(s) + Hydrochloric acid(aq) → Magnesium chloride(aq) + Hydrogen(g)
6. What happens when dilute hydrochloric acid is added to iron fillings? Tick the correct answer.
a. Hydrogen gas and iron chloride are produced.
b. Chlorine gas and iron hydroxide are produced.
c. No reaction takes place.
d. Iron salt and water are produced.
7. Any three difference between acids and bases?
8. Which gas is usually liberated when an acid reacts with a metal? Illustrate with an example. How will you test for the presence of this gas?
9. Metal compound A reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride.
10. Why does an aqueous solution of an acid conduct electricity?
11. What effect does the concentration of H+(aq) ions have on the nature of the solution?
12. Write down Uses of sodium hydrogen carbonate (NaHCO3)
13. Write down make process of Plaster of Paris (POP).
14. Write an equation to show the reaction between Plaster of Paris and water.
15. Why does distilled water not conduct electricity, whereas rain water does?
16. What is a neutralisation reaction? Give two examples.
17. Explain the meanings of malleable and ductile.
18. Why is sodium kept immersed in kerosene oil?
19. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4.
20. Write the electron-dot structures for sodium, oxygen and magnesium.
21. Name two metals which are found in nature in the free state.
22. Which metals do not corrode easily?
23. What are alloys?
24. What are amphoteric oxides? Give two examples of amphoteric oxides.
25. Name two metals which will displace hydrogen from dilute acids, and two metals which will not.
26. Give reasons why copper is used to make hot water tanks and not steel (an alloy of iron).
27. What would be the electron dot structure of carbon dioxide which has the formula CO2?
28. How many structural isomers can you draw for pentane?
29. What will be the formula and electron dot structure of cyclopentane?
30. A mixture of oxygen and ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is not used?
31. What are oxidising agents?
32. How would you distinguish experimentally between an alcohol and a carboxylic acid?
33. Would you be able to check if water is hard by using a detergent?
34. What is an homologous series? Explain with an example.
35. How can ethanol and ethanoic acid be differentiated on the basis of their physical and chemical properties?
36. Which of the following hydrocarbons undergo addition reactions:
C2H6, C3H8, C3H6, C2H2 and CH4.
37. Give a test that can be used to differentiate chemically between butter and cooking oil.
38. What were the limitations of Döbereiner’s classification?
39. Besides gallium, which other elements have since been discovered that were left by Mendeléev in his Periodic Table? (any two)
40. Why do you think the noble gases are placed in a separate group?
41. Name two elements you would expect to show chemical reactions similar to magnesium. What is the basis for your choice?
42. In the Modern Periodic Table, which are the metals among the first ten elements?
43. In the Modern Periodic Table, calcium (atomic number 20) is surrounded by elements with atomic numbers 12, 19, 21 and 38. Which of these have physical and chemical properties resembling calcium?
44. Lithium, sodium, potassium are all metals that react with water to liberate hydrogen gas. Is there any similarity in the atoms of these elements?
45. What criteria do we use to decide whether something is alive?
46. What are outside raw materials used for by an organism?
47. What processes would you consider essential for maintaining life?
48. What are the differences between autotrophic nutrition and heterotrophic nutrition?
49. How is the small intestine designed to absorb digested food?
50. What are the different ways in which glucose is oxidised to provide energy in various organisms?
51. How are the lungs designed in human beings to maximise the area for exchange of gases?
52. Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
53. What are plant hormones?
54. How do auxins promote the growth of a tendril around a support?
55. Why is the use of iodised salt advisable?
56. Why are some patients of diabetes treated by giving injections of insulin?
57. How does phototropism occur in plants?
58. How does chemical coordination occur in plants?
59. What is the difference between the manner in which movement takes place in a sensitive plant and the movement in our legs?
60. How are involuntary actions and reflex actions different from each other?
61. What is the importance of DNA copying in reproduction?
62. How will an organism be benefited if it reproduces through spores?
63. Why is DNA copying an essential part of the process of reproduction?
64. What is the role of the seminal vesicles and the prostate gland?
65. What are the different methods of contraception?
66. What could be the reasons for adopting contraceptive methods?
67. Draw a labelled diagram of the longitudinal section of a flower.
68. What are the functions performed by the testis in human beings?
69. How does the creation of variations in a species promote survival?
70. How do Mendel’s experiments show that traits are inherited independently?
71. How is the sex of the child determined in human beings?
72. What are the different ways in which individuals with a particular trait may increase in a population?
73. What factors could lead to the rise of a new species?
74. What are fossils? What do they tell us about the process of evolution?
75. In evolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
76. Explain the importance of fossils in deciding evolutionary relationships.
77. How is the equal genetic contribution of male and female parents ensured in the progeny?
78. What evidence do we have for the origin of life from inanimate matter?
79. Outline a project which aims to find the dominant coat colour in dogs.
80. The radius of curvature of a spherical mirror is 20 cm. What is its focal length?
81. Why do we prefer a convex mirror as a rear-view mirror in vehicles?
82. A convex mirror used for rear-view on an automobile has a radius of curvature of 3.00 m. If a bus is located at 5.00 m from this mirror, find the position, nature and size of the image.
83. A concave mirror produces three times magnified (enlarged) real image of an object placed at 10 cm in front of it. Where is the image located?
84. Light enters from air to glass having refractive index 1.50. What is the speed of light in the glass? The speed of light in vacuum is 3 × 108 m s-1.
85. A concave lens has focal length of 15 cm. At what distance should the object from the lens be placed so that it forms an image at 10 cm from the lens? Also, find the magnification produced by the lens.
86. A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.
87. Find the power of a concave lens of focal length 2 m.
88. One-half of a convex lens is covered with a black paper. Will this lens produce a complete image of the object? Verify your answer experimentally. Explain your observations.
89. A doctor has prescribed a corrective lens of power +1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging?
90. What is the phenomenon responsible for the blue colour of sky?
91. What is the near and far point of a normal eye?
92. Name the component of eye that is responsible for the adjustment of eyelens?
93. To an astronaut why does the sky appear dark instead of blue?
94. Why the star twinkle but not earth?
95. Draw the labelled diagram of human eye and explain the image formation?
96. What is power of accommodation? How ciliary muscles helps in accommodation?
97. Explain the function of
a. Iris
b. Pupil
c. Retina
98. Calculate the number of electrons constituting one coulomb of charge.
99. Define the unit of current.
100. What is meant by saying that the potential difference between two points is 1 V?
101. The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V?
102. A wire of given material having length l and area of cross-section A has a resistance of 4
. What would be the resistance of another wire of the same material having length l/2 and area of cross-section 2A?
. What would be the resistance of another wire of the same material having length l/2 and area of cross-section 2A?103. Why are coils of electric toasters and electric irons made of an alloy rather than a pure metal?
104. An electric lamp, whose resistance is 20 Ω, and a conductor of 4 
resistance are connected to a 6 V battery Calculate (a) the total resistance of the circuit, (b) the current through the circuit, and (c) the potential difference across the electric lamp and conductor.
resistance are connected to a 6 V battery Calculate (a) the total resistance of the circuit, (b) the current through the circuit, and (c) the potential difference across the electric lamp and conductor.105. In the circuit diagram given in Fig. 12.10, suppose the resistors R1, R2 and R3 have the values 
respectively, which have been connected to a battery of 12 V. Calculate (a) the current through each resistor, (b) the total current in the circuit, and (c) the total circuit resistance.
respectively, which have been connected to a battery of 12 V. Calculate (a) the current through each resistor, (b) the total current in the circuit, and (c) the total circuit resistance.106. What are the advantages of connecting electrical devices in parallel with the battery instead of connecting them in series?
107. What is (a) the highest, (b) the lowest total resistance that can be secured by combinations of four coils of resistance 
?
?108. An electric iron of resistance 
takes a current of 5 A. Calculate the heat developed in 30 s.
takes a current of 5 A. Calculate the heat developed in 30 s.109. An electric refrigerator rated 400 W operates 8 hour/day. What is the cost of the energy to operate it for 30 days at Rs 3.00 per kW h?
110. How many 
resistors (in parallel) are required to carry 5 A on a 220 V line?
resistors (in parallel) are required to carry 5 A on a 220 V line?111. Compare the power used in the 
resistor in each of the following circuits: (i) a 6 V battery in series with 
and resistors, and (ii) a 4 V battery in parallel with 
and resistors.
resistor in each of the following circuits: (i) a 6 V battery in series with and resistors, and (ii) a 4 V battery in parallel with and resistors.112. An electric heater of resistance 8
draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.
draws 15 A from the service mains 2 hours. Calculate the rate at which heat is developed in the heater.113. Why is the series arrangement not used for domestic circuits?
114. A current through a horizontal power line flows in east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?
115. List the properties of magnetic lines of force.
116. Why don’t two magnetic lines of force intersect each other?
117. Choose the correct option.The magnetic field inside a long straight solenoid-carrying current
a. is zero.
b. decreases as we move towards its end.
c. increases as we move towards its end.
d. is the same at all points.
118. State Fleming’s left-hand rule.
119. What is the role of the split ring in an electric motor?
120. Explain different ways to induce current in a coil.
121. Name some sources of direct current.
122. Which sources produce alternating current?
123. An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
124. List two methods of producing magnetic fields.
125. When is the force experienced by a current–carrying conductor placed in a magnetic field largest?
126. Name some devices in which electric motors are used.
127. When does an electric short circuit occur?
128. Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
129. What is a good fuel?
130. If you could use any source of energy for heating your food, which one would you use and why?
131. How has the traditional use of wind and water energy been modified for our convenience?
132. What is geothermal energy?
133. What are the advantages of nuclear energy?
134. Hydrogen has been used as a rocket fuel. Would you consider it a cleaner fuel than CNG? Why or why not?
135. What are the qualities of an ideal source of energy?
136. What are the environmental consequences of the increasing demand for energy? What steps would you suggest to reduce energy consumption?
137. Give any two ways in which biodegradable substances would affect the environment.
138. Give any two ways in which non-biodegradable substances would affect the environment.
139. What is the role of decomposers in the ecosystem?
140. What is ozone and how does it affect any ecosystem?
141. What are the problems caused by the non-biodegradable wastes that we generate?
142. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
143. What would be the advantages of exploiting resources with short-term aims?
144. Why do you think there should be equitable distribution of resources? What forces would be working against an equitable distribution of our resources?
145. Compare the above system with the probable systems in hilly/ mountainous areas or plains or plateau regions.
146. How can you as an individual contribute or make a difference to the management of (a) forests and wildlife, (b) water resources and (c) coal and petroleum?
147. Explain the 3R.
148. What changes would you suggest in your home in order to be environment-friendly?
149. List five things you have done over the last one week to –
a. conserve our natural resources.
b. increase the pressure on our natural resources.
150. Why should we conserve forests and wildlife?
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