10th CBSE Science Pre Board Exam 2020-21
General Instructions: 10th CBSE Science Pre Board Exam 2020-21
- The question paper comprises four sections A, B, C and D. There are 36 questions in the question paper. All questions are compulsory.
- Section–A – question no. 1 to 20 – all questions and parts thereof are of one mark each.
- These questions contain multiple choice questions (MCQs), very short answer questions and assertion – reason type questions. Answers to these should be given in one word or one sentence.
- Section–B – question no. 21 to 26 are short answer type questions, carrying 2 marks each.
- Answers to these questions should in the range of 30 to 50 words.
- Section–C – question no. 27 to 33 are short answer type questions, carrying 3 marks each.
- Answers to these questions should in the range of 50 to 80 words.
- Section–D – question no. 34 to 36 are long answer type questions carrying 5 marks each.
- Answer to these questions should be in the range of 80 to 120 words.
- There is no overall choice. However, internal choices have been provided in some questions.
- A student has to attempt only one of the alternatives in such questions.
- Wherever necessary, neat and properly labeled diagrams should be drawn.
Question 1: List any two observations when lead nitrate is heated in a dry test tube?
A shiny brown coloured element X on heating in air becomes black in colour. Name the element X and the black coloured compound formed.
Question 2: What is a cure for bee sting?
Question 3: Which element has twice as many electrons in its second shell as in its first shell?
Question 4: Write balanced chemical equation for – dilute sulphuric acid reacts with aluminum powder.
Question 5: Mention the condition under which a current can flow in a conductor.
Question 6: List two examples of STDs caused due to viral infection.
What is placenta?
Question 7: What is the full form of IUCD?
Question 8: Which component of white light is least scattered by fog or smog
Question 9: Name the physical quantity which is (a) same (b) different in all the bulbs when three bulbs of different wattage are connected in series.
Calculate the electric current in the given circuit when both the keys are closed.
Question 10: Which phenomenon is responsible for making the path of light visible?
Question 11: Draw electron dot structure of ethane.
Question 12: When is the force experienced by a current carrying conductor placed in a magnetic field largest?
State the rule to determine the direction of a force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
Question 13: Write the aquatic organisms in order of who eats whom starting from producer and form a chain of at least three steps.
Give reason why the existence of decomposers is essential in a biosphere.
For question numbers 14, 15 and 16, two statements are given – one labeled Assertion (A) and the other labeled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below:
a) Both A and R are true, and R is correct explanation of the assertion.
b) Both A and R are true, but R is not the correct explanation of the assertion.
c) A is true, but R is false.
d) A is false, but R is true.
Question 14: Assertion: Sun appears reddish in the morning. It will not be observed on moon.
Reason: It is because moon does not have atmosphere, therefore, red light will not scatter.
Question 15: Assertion: The opening and closing of stomata is controlled by guard cells.
Reason: The pore is the site for exchange of gases in plants.
Assertion: Veins have thin walls to collect blood from different organs.
Reason: Blood in veins are not under pressure.
Question 16: Assertion: NaHCO3 is a basic salt.
Reason: It is a salt of strong base NaOH and weak acid H2CO3.
Question 17 to 20 contains five sub parts. You are required to answer any four sub parts in these questions.
Only flowering plants undergo the process of pollination. After pollination there is the formation of pollen tube which helps in transferring of male gametes up to an egg cell. Female egg cells are present in the ovules present in the ovary of the female pistil while male gametes are present in the pollen grains. When the pollen tubes after passing though the style reaches the ovules in the ovary, the male gametes enter the embryo sac and fertilization takes place. In fertilization there is no such requirement apart from the male gamete and female gamete. The fertilized egg fuse to become the zygote which develops into an embryo.
- What is pollination?
- What are the requirements for pollination?
- What is zygote?
- Trace the events taking place after pollination till fertilization.
- Which part of pistil mature into fruit?
Question 18: The electrolysis is a process in which the solution or molten liquid allows electricity to pass through it. The electrolysis of acid and water conducts electricity and the bulb glows as the circuit is complete.
- Infer the result if alcohol is used instead of acid.
- If the acid is replaced by glucose will the bulb glow? Explain.
- Name the ions produced during the electrolysis of HCL.
- Define electrolysis.
- What will happen if you will replace the above situation in the beaker with molten sodium chloride?
Question 19: Study the graph and answer the following questions.
- Where do we use the chemicals that would release the harmful chemicals in the air?
- Why the emission of harmful gases was less in 1960’s & 2010 onwards?
- Which chemical depletes ozone layer?
- In which year was the ozone depletion maximum?
- What is the full form of CFC?
Question 20: In 1827, a German physicist Georg Ohm found the relationship between the current I flowing in a metallic wire & the potential difference across its terminal. The potential difference, V across the ends of a given metallic wire in electric circuit is directly proportional to current following though it, provided temperature remains the same. This is called Ohm’s law.
- Write the expression of Ohm’s law.
- What is resistance?
- Show graph between V versus I.
- Calculate voltage when current is 0.6A & the resistance is 10 Ohm.
- How does resistance depend on temperature?
SECTION B: 10th CBSE Science Pre Board Exam 2020-21
Question 21: Write the function of the following parts in human female reproductive system.
Draw a well labeled diagram of human male reproductive system.
Question 22: Draw a ray diagram of an object when an object placed between F1 and 2F1 in front of convex lens.
Question 23: ‘The breathing cycle is rhythmic whereas exchange of gases is a continuous process.’ Justify this statement.
Question 24: Why does sky look blue on a clear day?
Explain the formation of rainbow with the help of a diagram.
Question 25: Properties of the elements are given below. Where would you locate the following elements in the periodic table?
- An element which is tetravalent and forms the basis of organic chemistry
- An element with variable (more than one) valency stored under water.
Question 26: Give reasons:
- Ionic compounds in general have high melting & boiling points.
- Sodium & Potassium are stored under oil.
Question 27: An object is placed at a distance of 10 cm from a convex mirror of focal length 15 cm. Find the position and nature of the image?
Question 28: Differentiate between aerobic and anaerobic respiration.
Question 29: If we cross pure bread tall pea plant with pure bread dwarf pea plant we will get pea plants of F1 generation. If we now self cross the pea plant of F1 generation, then we obtain pea plants of F2 generation.
- What do the plants of F1 generation look like?
- State the ratio of tall plants to dwarf plants in F2 generation.
- State the type of plants not found in F1 generation but appeared in F2 generation, mentioning the reason for the same.
In humans, there is a 50% probability of the birth of a boy and 50% probability that a girl will be born. Justify the statement on the basis of the mechanism of sex-determination in human beings.
Question 30: A metal X, which is used in thermite process when heated with oxygen gives an oxide Y which is amphoteric in nature. Identify X and Y. Write down the reactions of oxide Y with HCL & NaOH.
Question 31: A piece of wire of resistance 20 ohm is drawn out so that its length is increased to twice its original length. Calculate the resistance of the wire in new situation.
Question 32: What is meant by homologous series of carbon compounds? Write the general formula of alkenes & alkynes. Give two characteristics of homologous series.
Question 33: Draw a well labeled diagram of human alimentary canal.
SECTION D: 10th CBSE Science Pre Board Exam 2020-21
- With the help of diagram explain binary fission in amoeba.
- List any two advantages of vegetative propagation
- Define the term puberty. List two changes observed in girls at the time of puberty.
- ‘The chromosome number of the sexually reproducing parents & their offspring is the same’. Justify this statement.
Question 35: Equal lengths of magnesium ribbon are taken in two test tubes A and B. H2SO4 is added to test tube A and H2CO3 in the test tube B in equal amounts.
- Identify the test tube shaving vigorous reaction. Give reason to support your answer.
- Name the gas liberated in both the test tubes. How will you prove its liberation?
- Write chemical equations for both reactions.
- Out of the two acids taken above which one will have lower pH value and lower hydrogen ion concentration
- Why and when does a current carrying conductor kept in a magnetic field experience force? List the factors on which direction of this force depends.
- The magnetic field associated with a current carrying straight conductor is in anticlockwise direction. If the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of current.
- What is the purpose of the soft iron core used in making an electromagnet? How is it different from the permanent magnet?
- A compass needle is placed near a current carrying wire. State your observation for the following cases and give reasons for the same in each case
i. Magnitude of electric current in the wire is increased.
ii. The compass needle is displaced away from the wire.