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NCERT 7th Class (CBSE) Science: Chemical and Chemical Changes

10 CBSE Science Pre-Board 2018-19

10th Science Pre-Board Question Paper (2018-19)

School Name: Venkateshwar Global School, Sector 13, Rohini, Delhi 110085 India
Time: 3 hours
M.M: 80
Subject Code: 086
Class: X
Subject: Science
Date: 20/02/2019

General Instructions:

  • The question paper comprises two sections, A, B, C, D and E. You are to attempt both the sections.
  • All questions are compulsory.
  • All questions of Section A, B, C, D and E are to be attempted separately.
  • Question numbers 1 & 2 in Section- A are 1 mark question. They are to be answered in one word in one sentence.
  • Question numbers 3 to 5 in Section- B are 2 marks questions. These are to be answered in 30 words each.
  • Question numbers 6 to 15 in Section-C are 3 marks questions. These are to be answered in about 50 words each.
  • Question numbers 16 to 21 in Section-D are 5 marks questions. These are to be answered in 70 words each.
  • Question numbers 22 to 27 in Section-E are based on practical skills. Each question is a two marks question. These are to be answered in brief.

Section A

Question: 1. List two advantages of water harvesting at the community level. [1]

Question: 2. State two sources of  magnetic field. [1]

Question: 3. A pencil when dipped in water in a glass tumbler, appears to be bent at the air-water interface. Give reason for the following, along with a diagram. [2]

Question: 4.

  1. How much work will be done in bringing a charge of 2 × 10-3 coulombs from infinity to a point P at which the potential is 5 V?
  2. How can three resistors of resistance 2Ω, 3Ω and 6Ω be connected to give a total resistance of 4Ω. [2]

Question: 5. From the following elements: 4Be, 9F, 19K, 20Ca

  1. Select two elements of the same group. Give justification for your selection.
  2. Write the formula and mention the nature of the compound formed by the union of K and element X (2, 8, 7) [2]

Question: 6. Write in brief how does a hydro power plant works. Give one advantage and one disadvantage of the same. [3]

Question: 7.

  1. Name and state the law which relates the angle of incidence and refraction for refraction between a pair of media.
  2. The refractive indices of kerosene, turpentine oil and water are 1.44, 1.47 and 1.33 respectively. Which of the following medium has (i) maximum optical density, (ii) maximum speed of light?
  3. Calculate speed of light in kerosene, given speed of light in vacuum is 3 × 108 m/s. [1+1+1]

Question: 8.

  1. Explain an activity to show that a current carrying conductor experiences a force when placed in a magnetic field.
  2. What change in the deflection of the compass needle at a point near current carrying straight conductor shall be observed in the:
    (i) Current through the conductor is increased?
    (ii) direction of current in the conductor is reversed? [3]

Question: 9.

  1. State the role of plant hormones. Name a plant hormone which is essential for cell division.
  2. Name and explain the role of plant hormone involved in phototropism. [1+2]

Question: 10.

  1. Identify the gland that secrete (a) insulin and (b) thyroxin.
  2. Explain with the help of an example how the timing and amount of hormone secreted are regulated in a human body. [1+2]

Question: 11.

  1. Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of the animals together to establish a common evolutionary origin? Justify your answer.
  2. “Birds have evolved from reptiles”. State evidence to prove the statements. [2+1]

Question: 12.

  1. How is ozone formed in the upper atmosphere? State how it affects an ecosystem.
  2. List two changes one can make in his/her habits to become more environment friendly. [2+1]

Question: 13.

  1. Draw electron dot structure of sodium oxide.
  2. Different between ionic and covalent compounds. (2 points each)
  3. Write preparation of a salt used for bleaching clothes. [1 × 3 = 3]

Question: 14.

  1. Explain different types of decomposition reactions with examples.
  2. ZnO + CO → Zn + CO2. Identify the reduced and oxidized substance. [2+1]

Question: 15.

  1. How are metals of high reactivity extracted from their ores?
  2. Differentiate between calcination and roasting. Also give examples. [1.5+1.5]

Question: 16.

  1. Explain why the sun appears reddish early in the morning.
  2. Why don’t the planets twinkle?
  3. Draw ray diagrams to show the defect and correction for a person suffering from far-sightedness. [1.5+1.5+2]

Question: 17.

  1. Two resistances when connected in parallel given result value of 2 ohm, when connected in series the value becomes 9 ohm. Calculate the value of each resistance.
  2. An electric iron has a rating of 750 W, 220 V. Calculate:
    (i) the current passing through it, and
    (ii) its resistance, when in use. [3+2]

Question: 18.

  1. Why metallic character increases on moving down the group?
  2. How does atomic size of element vary while going from left to right along a period in the Modern periodic table?
  3. Explain giving example that number of valence electrons in a group are same.
  4. Why are group 18 elements considered as inert?
  5. Explain Dobereiner’s Triad. [5×1 = 5]

Question: 19.

  1. Write a chemical equation to covert ethanol to ethanoic acid.
  2. Explain the esterification and saponifications reactions along with their equations.
  3. Explain the mechanism for cleansing action of soap with the help of a diagram. [1+2+2]

Question: 20.

  1. Draw a sectional view of the human alimentary canal and label the following parts:
    (a) Oesophagus   (b) Liver    (c) Pancreas    (d) Stomach
  2. What is meant by term peristalsis? [4+1]

Question: 21.

  1. Write the functions of the following in human female reproductive system Ovary, Oviduct and Uterus.
  2. What is placenta? State its major role in case of a pregnant human female. [3+2]

Section B (Practical questions)

Question: 22. Draw the ray diagram when a light ray is incident on a glass prism. Mention clearly the angle of incidence, emergence and deviation. [2]

Question: 23. In a voltmeter, there are 20 divisions between the 0 marks an 0.5 V mark. What is the least count of the voltmeter? How is it connected in circuit? [2]

Question: 24. What is hard and soft water? How can we check hardness of water? [2]

Question: 25. Write reaction involved between HCl and NaOH individually with

  1. Zn metal
  2. NaHCO [2]

Question: 26. While preparing a temporary mount of a leaf to show its stomata, list four precautions which are suggested to be observed to get better result [2]

Question: 27. Name the type of asexual reproduction in which parent identity is lost. Draw the initial and final stages of this type of reproduction. State the event with which this reproduction starts. [2]

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