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# Board Paper of Class 10 2019 Science Delhi(Set 3) - 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 1
If you could use any source of energy for heating your food which one would you prefer? State one reason for your choice. VIEW SOLUTION

• Question 2
Write the function of voltmeter in an electric circuit. VIEW SOLUTION

• Question 3
What happens to the image distance in the normal human eye when we decrease the distance of an object, say 10 m to 1 m ? Justify your answer. VIEW SOLUTION

• Question 4
List two different functions performed by pancreas in our body. VIEW SOLUTION

• Question 5
How it can be proved that the basic structure of the Modern Periodic Table is based on the electronic configuration of atoms of different elements?

OR

The electronic configuration of an element is 2, 8, 4. State its:
(a) group and period in the Modern Periodic Table.
(b) name and write its one physical property. VIEW SOLUTION

• Question 6

How can we help in reducing the problem of waste disposal? Suggest any three methods.

OR

Define an ecosystem. Draw a block diagram to show the flow of energy in an ecosystem.

VIEW SOLUTION

• Question 7
List three advantages each of:
(i) exploiting resources with short term aims, and
(ii) using a long term perspective in managing our natural resources. VIEW SOLUTION

• Question 8
What is a rainbow? Draw a labelled diagram to show the formation of a rainbow. VIEW SOLUTION

• Question 9
Nervous and hormonal systems together perform the function of control and coordination in human beings. Justify this statement with the help of an example. VIEW SOLUTION

• Question 10
Trace the sequence of events which occur when a bright light is focused on your eyes. VIEW SOLUTION

• Question 11
What is photosynthesis? Explain its mechanism. VIEW SOLUTION

• Question 12
Name the plant Mendel used for his experiment. What type of progeny was obtained by Mendel in F1 and F2 generations when he crossed the tall and short plants? Write the ratio he obtained in F2 generation plants.

OR

List two differences between acquired traits and inherited traits by giving an example of each. VIEW SOLUTION

• Question 13
2 g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime. What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation. Identify the type of chemical reaction.
OR
Identify the type of reactions taking place in each of the following cases and write the balanced chemical equation for the reactions.
(a) Zinc reacts with silver nitrate to produce zinc nitrate and silver.

(b) Potassium iodide reacts with lead nitrate to produce potassium nitrate and lead iodide.
VIEW SOLUTION

• Question 14
Based on the group valency of elements write the molecular formula of the following compounds giving justification for each:
(i) Oxide of first group elements.
(ii) Halide of the elements of group thirteen, and
(iii) Compound formed when an element, A of group 2 combines with an element, B of group seventeen. VIEW SOLUTION

• Question 15
Explain the following:

(a) Sodium chloride is an ionic compound which does not conduct electricity in solid state. However, it does conduct electricity in molten state as well as in aqueous solution.

(b) Reactivity of aluminium decreases if it is dipped in nitric acid.

(c) Metals like calcium and magnesium are never found in their free state in nature. VIEW SOLUTION

• Question 16
(a) With the help of a suitable circuit diagram prove that the reciprocal of the equivalent resistance of a group of resistances joined in parallel is equal to the sum of the reciprocals of the individual resistances.

(b) In an electric circuit, two resistors of 12 Ω each are joined in parallel to a 6 V battery. Find the current drawn from the battery.

OR

An electric lamp of resistance 20 Ω and a conductor of resistance 4 Ω are connected to a 6 V battery as shown in the circuit. Calculate: (a) the total resistance of the circuit,

(b) the current through the circuit,

(c) the potential difference across the (i) electric lamp and (ii) conductor, and

(d) power of the lamp. VIEW SOLUTION

• Question 17
(a) Draw magnetic field lines produced around a current carrying straight conductor passing through cardboard. Name, state and apply the rule to mark the direction of these field lines.
(b) How will the strength of the magnetic field change when the point where magnetic field is to be determined is moved away from the straight wire carrying constant current? Justify your answer. VIEW SOLUTION

• Question 18
An object is placed at a distance of 60 cm from a concave lens of focal length 30 cm.
(i) Use lens formula to find the distance of the image from the lens.
(ii) List four characteristics of the image (nature, position, size, erect/inverted) formed by the lens in this case.
(iii) Draw ray diagram to justify your answer of part (ii).  VIEW SOLUTION

• Question 19
Define pollination. Explain the different types of pollination. List two agents of pollination? How does suitable pollination lead to fertilization?
OR
(a) Identify the given diagram. Name the parts 1 to 5. (b) What is contraception? List three advantages of adopting contraceptive measures. VIEW SOLUTION

• Question 20
Write the chemical formula and name of the compound which is the active ingredient of all alcoholic drinks. List its two uses. Write chemical equation and name of the product formed when this compound reacts with−
(i) Sodium metal
(ii) hot concentrated sulphuric acid
OR
What is methane? Draw its electron dot structure. Name the type of bonds formed in this compound. Why are such compounds:
(i) poor conductors of electricity? and
(ii) have low melting and boiling points? What happens when this compound burns in oxygen? VIEW SOLUTION

• Question 21
Write the main difference between an acid and a base. With the help of suitable examples explain the term neutralization and the formation of -
(i) acidic,
(ii) basic and
(iii) neutral salts VIEW SOLUTION

• Question 22
In the experimental set up to show that "CO2 is given out during respiration", name the substance taken in the small test tube kept in the conical flask. State its function and the consequence of its use. VIEW SOLUTION

• Question 23
A student is observing the temporary mount of a leaf peel under a microscope. Draw labelled diagram of the structure of stomata as seen under the microscope
OR
Draw a labelled diagram in proper sequence to show budding in hydra.
VIEW SOLUTION

• Question 24
List four precautions which a student should observe while determining the focal length of a given convex lens by obtaining image of a distant object on a screen. VIEW SOLUTION

• Question 25
While studying the dependence of potential difference (V) across a resistor on the current (I) passing through it, in order to determine the resistance of the resistor, a student took 5 readings for different values of current and plotted a graph between V and I. He got a straight line graph passing through the origin. What does the straight line signify? Write the method of determining the resistance of the resister using this graph.

OR

What would you suggest to a student if while performing an experiment he finds that the pointer/needle of the ammeter and voltmeter do not coincide with the zero marks on the scales when the circuit is open? No extra ammeter/voltmeter is available in the laboratory. VIEW SOLUTION

• Question 26
In three test tubes A, B, and C, three different liquids namely, distilled water, underground water and distilled water in which a pinch of calcium sulphate is dissolved, respectively are taken. Equal amount of soap solution is added to each test tube and the contents are shaken. In which test tube will the length of the foam (lather) be longest? Justify your answer. VIEW SOLUTION

• Question 27
Blue litmus solution is added to two test tubes A and B containing dilute HCl and NaOH solution respectively. In which test tube a colour change will be observed? State the colour change and give its reason.

OR

What is observed when 2 mL of dilute hydrochloric acid is added to 1 g of sodium carbonate taken in a clean and dry test tube? Write chemical equation for the reaction involved. VIEW SOLUTION
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