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# Board Paper of Class 10 2019 Science Abroad(Set 2) - Solutions

General Instructions:

(i) The question paper comprises five sections, A, B, C, D and E. You are to attempt all the sections.

(ii) All questions are compulsory.

(iii) Internal choice is given in sections B, C, D and E.

(iv) Question numbers 1 and 2 in Section A are one mark questions. They are to be answered in one word or in one sentence.

(v) Question numbers 3 to 5 in Section B are two-marks questions. These are to be answered in about 30 words each.

(vi) Question numbers 6 to 15 in Section C are three-marks questions. These are to be answered in about 50 words each.

(vii) Question numbers 16 to 21 in Section D are five-marks questions. These are to be answered in about 70 words each.

(viii) 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.

• Question 2
Name the component of sunlight which facilitates drying of wheat after harvesting. VIEW SOLUTION

• Question 3
State laws of refraction of light.
OR

List four characteristics of the image formed by a concave mirror of focal length 40 cm when the object is placed in front of it at a distance of 20 cm from its pole. VIEW SOLUTION

• Question 4
Draw magnetic field lines in and around a current carrying straight solenoid. VIEW SOLUTION

• Question 5
Write the name and molecular formula of a carbon compound having its name suffixed with "-ol" and having two carbon atoms in its molecule. With the help of a chemical equation indicate what happens when this compound is heated with excess conc. H2SO4. VIEW SOLUTION

• Question 6
Define the term evolution. "Evolution cannot be equated with progress." Give examples to justify this statement. VIEW SOLUTION

• Question 7
(a) Plants do not have any nervous system but yet, if we touch a sensitive plant, some observable changes take place in its leaves. Explain how could this plant respond to the external stimuli and how it is communicated.

(b) Name the hormone that needs to be administered to
(i) increase the height of a dwarf plant.
(ii) cause rapid cell division in fruits and seeds. VIEW SOLUTION

• Question 8
(a) Write the function of the following in the human alimentary canal:
(i) Saliva
(ii) HCl in stomach
(iii) Bile juice
(iv)Villi

(b) Write one function each of the following enzymes:
(i) Pepsin
(ii) Lipase VIEW SOLUTION

• Question 9
Salt 'P', commonly used in bakery products, on heating gets converted into another salt 'Q' which itself is used for the removal of hardness of water and a gas 'R' is evolved. The gas 'R' when passed through freshly prepared lime water turns milky. Identify 'P', 'Q' and 'R', giving chemical equation for the justification of your answer. VIEW SOLUTION

• Question 10
Classify the following reactions into different types:
(i) AgNO3(aq) + NaCl(aq) →AgCl(s) + NaNO3(aq)

(ii) CaO(s) + H2O(l) → Ca(OH)2(aq)

(iii) $2{\mathrm{KClO}}_{3}\left(\mathrm{s}\right)\stackrel{∆}{\to }2\mathrm{KCl}\left(\mathrm{aq}\right)+3{\mathrm{O}}_{2}\left(\mathrm{g}\right)$

(iv) Zn + CuSO4 → ZnSO4 + Cu

(b) Translate the following statement into a balanced chemical equation:

"Barium chloride reacts with aluminium sulphate to give aluminium chloride and barium sulphate."

OR

When potassium iodide solution is added to a solution of lead (II) nitrate in a test tube, a precipitate is formed.

(a) What is the colour of this precipitate? Name the compound precipitated.

(b) Write the balanced chemical equation for this reaction.

(c) List two types of reactions in which this reaction can be placed. VIEW SOLUTION

• Question 11
How is the method of extraction of metals high up in the reactivity series different from that for metals in the middle? Why can the same process not be applied for them? Name the process used for the extraction of these metals. VIEW SOLUTION

• Question 12
The following diagram shows two parallel straight conductors carrying same current. Copy the diagram and draw the pattern of the magnetic field lines around them showing their directions. What is the magnitude of magnetic field at a point 'X' which is equidistant from the conductors? Give justification for your answer.

VIEW SOLUTION

• Question 13
What is the cause of dispersion of white light through a glass prism? Draw a ray diagram to show the path of light when two identical glass prisms are arranged together in an inverted position with respect to each other and a narrow beam of white light is allowed to fall obliquely on one of the faces of the prisms.
OR

What is the scattering of light? Use this phenomenon to explain why (i) the Sun appears reddish at sun-rise, and (ii) the clear sky appears blue. VIEW SOLUTION

• Question 14
(a) Natural water bodies are not regularly cleaned whereas an aquarium needs regular cleaning. Why?

(b) What are decomposers? What will be the consequence if the decomposers are completely eradicated from an ecosystem? Give justification in support of your answer.
OR
How is ozone formed in the upper atmosphere? State its importance. What is responsible for its depletion? Write one harmful effect of ozone depletion. VIEW SOLUTION

• Question 15
What is exploitation of resources with short term aims? List its four advantages. VIEW SOLUTION

• Question 16
(a) If we cross pure-bred tall (dominant) pea plants with pure-bred dwarf (recessive) pea plants we get pea plants of F1 generation. If we now self-cross the pea plants of F1 generation, then we obtain pea plants of F2 generation.
(i) What do the plants of F1 generation look like?
(ii) What is the ratio of tall plants to dwarf plants in F2 generation?
(iii) State the type of plants not found in Fgeneration but appeared in F2 generation, mentioning the reason for the same.

(b) What are homologous structures? Give an example. Is it necessary that homologous structures always have common ancestors? VIEW SOLUTION

• Question 17
(a) Define vegetative propagation. List its two methods.
(b) Why is this mode practised for growing some types of plants?
(c) Explain the process of budding in Hydra with the help of labelled diagrams.
OR
What is contraception? List its four different methods. State four reasons for adopting contraceptive methods. VIEW SOLUTION

• Question 18
(a) List two limitations of Newlands' Law of Octaves.

(b) Write the electronic configuration of two elements A and B whose atomic numbers are 20 and 17 respectively. Write the molecular formula of the compound formed when element A reacts with element B. State whether this compound is acidic, basic or neutral. Give reason to justify your answer. VIEW SOLUTION

• Question 19
(a) Distinguish between esterification and saponification reactions with the help of chemical equations for each.
(b) With a labelled diagram describe in brief an activity to show the formation of ester.
OR
What is the difference between soaps and detergents? State in brief the cleansing action of soaps in removing an oily spot from a fabric. Why are soaps not very effective when a fabric is washed in hard water? How is this problem resolved? VIEW SOLUTION

• Question 20
(a) Define electric power. An electrical device of resistance R is connected across a source of voltage V and draws a current I. Derive an expression for power in terms of current and resistance.
(b) Two electric bulbs rated 100 W; 220 V and 60 W; 220 V are connected in parallel to electric mains of 220 V. Find the current drawn by the bulbs from the mains.
OR

(a) How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistors R1, R2 and R3 in series connected to a battery of V volts?

(b) Study the following circuit and find out:
(i) Current in 12 Ω resistor.
(ii) The difference in the readings of A1 and A2, if any.
VIEW SOLUTION

• Question 21
A person is unable to see objects distinctly placed within 50 cm from his eyes.
(a) Name the defect of vision the person is suffering from and list its two possible causes.
(b) Draw a ray diagram to show the defect in the above case.
(c) Mention the type of lens used by him for the correction of the defect and calculate its power. Assume that the near point for the normal eye is 25 cm.
(d) Draw a labeled diagram for the correction of the defect in the above case. VIEW SOLUTION

• Question 22
Which one of the following is the correct set-up for studying the dependence of the current on the potential difference across a resistor and why?
VIEW SOLUTION

• Question 23
Study the following ray diagram and list two mistakes committed by the student while tracing it. Rectify these mistakes by drawing the correct ray diagram to show the real position and size of the image corresponding to the position of the object AB.

OR

A student has to trace the path of a ray of light through a glass prism. List four precautions he should observe for better results.
VIEW SOLUTION

• Question 24
List two observations on the basis of which it may be concluded that the given slide shows binary fission in Amoeba. VIEW SOLUTION

• Question 25
Write four sequential steps of the procedure of the experiment "Preparing a temporary mount of a leaf peel to show stomata."
OR
In the experimental set-up to show that "the germinating seeds give out carbon dioxide", answer the following questions:
(i) Why do we keep the conical flask airtight?
(ii) Name the substance kept in the small test tube inside the conical flask. Write its role.
(iii) Why does water rise in the delivery tube? VIEW SOLUTION

• Question 26
A student mixes sodium sulphate powder in barium chloride powder. What change would the student observe on mixing the two powders? Justify your answer and explain how he can obtain the desired change.
OR
(a) Arrange the following metals in the increasing order of their reactivities:
Copper, Zinc, Aluminium and Iron
(b) List two observations you would record in your notebook 30 minutes after adding iron fillings to copper sulphate solution.
VIEW SOLUTION

• Question 27
A solution 'X' gives orange colour when a drop of it falls on pH paper, while another solution 'Y' gives bluish colour when a drop of it falls on pH paper. What is the nature of both the solutions? Determine the pH of solutions 'X' and 'Y'. VIEW SOLUTION
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