These sample papers have been taken from CBSE Board
Question 1: Which type of lens is used for the correction of myopia?
Answer: Concave lens
Question 2: What is the meaning of power of accommodation of human eye?
Answer: Human eye has the capability to clearly see a nearby object as well as a distant object. This capability of human eye is called power of accommodation.
Question 3: An aqueous solution of a substance ‘P’ is used in white washing. Name the substance ‘P’ and write its chemical formula. Also write the chemical equation for the reaction of substance ‘P’ with water.
Answer: Substance ‘P’ is washing soda (Sodium carbonate)
Chemical Formula of Washing Soda = Na2CO3
Reaction between sodium carbonate and water is given by following equation:
Question 4: List two energy sources that you would consider to be renewable. Give reasons for your choice.
Answer: Wind is circulated by various natural processes and takes negligible time. The sun keeps on emitting solar energy continuously. Hence, both solar energy and wind energy can be considered as renewable sources of energy.
Question 5: What are trophic levels? Make a food chain of four trophic levels.
Answer: Different levels in the food chain are called trophic levels. Following is a food chain with four trophic levels:
Grass → Grasshopper → Frog → Snake
Question 6: Write the chemical formula of bleaching powder. How is it prepared? Write balanced chemical equation for the reaction involved. Write one important use of bleaching powder.
Answer: Formula of Bleaching Powder: CaOCl2
Preparation of Bleaching Powder: When calcium hydroxide (slaked lime) reacts with chlorine, it gives calcium oxychloride (bleaching powder) and water is formed.
`Ca(OH)_2 + Cl_2 → CaOCl_2 + H_2O`
One Important Use of Bleaching Powder: As disinfectant for cleaning water
A sulphate salt of group two element of the periodic table is white, soft substance, which can be moulded into different shapes by making it dough. When this compound is left in open for sometime, it becomes a solid object and cannot be used for moulding purposes. Identify this sulphate salt and explain why does it show such a behaviour. Also give the equation for the reaction involved.
Answer: This substance is Plaster of Paris. When it reacts with water, it turns into gypsum which is a hard substance. Due to this, when plaster of Paris is left in open for some time, it absorbs moisture and turns into hard solid. The reaction is as follows:
`CaSO_4.(0.5)H_2O + (1.5)H_2O→ Ca\SO_4\(0.2)H_2O`
Question 7: Distinguish between ethanol and ethanoic acid on the basis of (i) litmus test and (ii) reaction with sodium hydrogen carbonate. Write the name and formula of the oxidizing agent used in the conversion of ethanol to ethanoic acid.
Answer: Ethanol changes red litmus to blue, while ethanoic acid changes blue litmus to red.
Ethanol does not react with sodium hydrogen carbonate, but ethanoic acid reacts with sodium hydrogen carbonate to give sodium acetate.
CH3COOH + NaHCO3 → CH3COONa + CO2 + H2
Potassium Permanganate (KMnO4) or Potassium Dichromate (K2Cr2O7) is used for conversion of ethanol to ethanoic acid.
Question 8: The elements Li, Na and K each having one valence electron are in the 2nd, 3rd and 4th period respectively of Modern Periodic Table.
Answer the following questions giving reasons:
(i) In which group should they be placed?
Answer: Group 1
(ii) Which one of these elements is least reactive?
(iii) Which one of these elements has the largest atomic radius?
Answer: Potassium (K)
(a) State the role performed by plant hormones. Name a plant hormone which is essential for cell division.
Answer: Plant hormones facilitate chemical coordination in plants. Cytokinin is essential for cell division.
(b) Name and explain the role of plant hormone involved in phototropism.
(a) Name the gland that secrete: (i) insulin, (ii) thyroxin
Answer: (i) Pancreas (ii) Thyroid gland
(b) Explain with an example how the timing and amount of hormone secreted are regulated in a human body.
Answer: Hormonal control is mainly based on feedback mechanism and tells the body to either pace up or slow down; as per the situation. So, timing and amount of hormone released by a particular gland depend upon the specific need of the situation. For example; adrenaline is released by adrenal gland when the body faces a stress situation. Amount of adrenaline to be released also depends on the degree of stress. Body gets ready accordingly as per the challenge it is going to face.
(a) Name the part of human brain which controls: (i) voluntary actions (ii) involuntary actions
Answer: (i) Cerebrum (ii) Medulla
(b) State the significance of peripheral nervous system. Name the components of this nervous system and distinguish between their origins.
Answer: Peripheral nervous system works as the conduit between the central nervous system and various organs of the body. Peripheral nervous system is composed of two types of nerves, viz. cranial nerves and spinal nerves. Cranial nerves come out of the brain, while spinal nerves come out of the nerve cord.
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