CBSE Class 10 Science 2020 Question Paper

Covalent compounds have low melting and boiling point. Why?

How many metals are present in second period of periodic table?

(a) What are geothermal energy hot-spots?

(b) Name two countries, other than India, where power plants based on geothermal energy are operational.

(c) Name the phenomenon that explains the working of an electric generator.

(d) State an important advantage of using AC over DC.

(a) Where is thyroid gland situated in our body?

(b) State the function of thyroxine in human body.

(c) What is hyperthyroidism?

(d) How can we control hypothyroidism?

Consider the following reasons for the reddish appearance of the sun at the sunrise or the sunset: A. Light from the sun near the horizon passes through thinner layers of air. B. Light from the sun covers larger distance of the earth's atmosphere before reaching our eyes. C. Near the horizon, most of the blue light and shorter wavelengths are scattered away by the particles. D. Light from the sun near the horizon passes through thicker layers of air. The correct reasons are

Person suffering from cataract has

The maximum resistance which can be made using four resistors each of $2\Omega$ is

A student plots V-I graphs for three samples of nichrome wire with resistances $R_1$, $R_2$ and $R_3$. Choose from the following the statement that holds true for this graph.

Which of the following are water intensive crops?

The most poisonous product formed by incomplete combustion of fossil fuels is

Bandharas and Tals are age old water harvesting concepts / structures found in

Identify 'x', 'y' and 'z' in the following reaction: $2\mathrm{KClO}_{3}(x)\xrightarrow{(y)}\mathrm{2KCl}(x)+\mathrm{O}_{2}(z)$

A visually challenged student, has to perform a lab test to detect the presence of acid in a given solution. The acid-base indicator preferred by him will be:

On the basis of electronic configuration of $\frac{9}{5}\mathrm{X}$, the group number and period of the element 'X' is:

An element 'X' with atomic number 11 forms a compound with element 'Y' with atomic number 8. The formula of the compound formed is

Assertion (A) : Ethanoic acid is also known as glacial acetic acid. Reason (R) : The melting point of pure ethanoic acid is 290 K and hence it often freezes during winters in cold climates.

Assertion (A) : The metals and alloys are good conductors of electricity. Reason (R) : Bronze is an alloy of copper and tin and it is not a good conductor of electricity.

A compound 'A' is used in the manufacture of cement. When dissolved in water, it evolves a large amount of heat and forms compound 'B'. (i) Identify A and B. (ii) Write chemical equation for the reaction of A with water. (iii) List two types of reaction in which this reaction may be classified.

Give reasons for the following: (i) Only one half of water molecule is shown in the formula of Plaster of Paris. (ii) Sodium hydrogen carbonate is used as an antacid. (iii) On strong heating, blue coloured copper sulphate crystals turn white.

OR: (i) Draw a labelled diagram to show the preparation of hydrogen chloride gas in laboratory. (ii) Test the gas evolved first with dry and then with wet litmus paper. In which of the two cases, does the litmus paper show change in colour? (iii) State the reason of exhibiting acidic character by dry HCl gas / HCl solution.

From the elements $^{39}_{19}\mathrm{A}$, $^{28}_{14}\mathrm{B}$, $^{16}_{8}\mathrm{C}$ and $^{40}_{18}\mathrm{D}$ identify: (a) the most electro positive element. (b) a noble gas. (c) a metalloid. (d) an element which will gain 2 electrons to attain nearest noble gas configuration. (e) formula of compound formed between A and C. (f) elements belonging to same period.

(a) Construct a terrestrial food chain comprising four trophic levels. (b) What will happen if we kill all the organisms in one trophic level? (c) Calculate the amount of energy available to the organisms at the fourth trophic level if the energy available to the organisms at the second trophic level is 2000 J.

OR: (a) Complete the following table: Oxygen, Ozone, Formula, (i), (ii), Benefits to biotic component, (iii), (iv). (b) How is ozone formed at the higher levels of atmosphere?

Complete the following flow chart as per the given instructions:

Explain giving an example how the following provide evidences in favour of evolution in organisms. (i) Homologous organs (ii) Fossils

What are chromosomes? Explain how in sexually reproducing organisms the number of chromosomes in the progeny is maintained.

What happens after refraction, when: (i) a ray of light parallel to the principal axis passes through a concave lens? (ii) a ray of light falls on a convex lens while passing through its principal focus? (iii) a ray of light passes through the optical centre of a convex lens?

Two coils of insulated copper wire are wound over a non-conducting cylinder as shown. Coil 1 has comparative large number of turns. State your observations, when (i) Key K is closed. (ii) Key K is opened. Give reason for each of your observations.

(a) List two causes of hypermetropia. (b) Draw ray diagrams showing (i) a hypermetric eye and (ii) its correction using suitable optical device.

OR: (a) State the relation between colour of scattered light and size of the scattering particle. (b) The apparent position of an object, when seen through the hot air, fluctuates or wavers. State the basic cause of this observation. (c) Complete the path of white light when it passes through two identical prisms placed as shown:

(a) How is the method of extraction of metals high up in the reactivity series different from that for metals in the middle? Why cannot the same process be applied for them? Name and explain the process of extraction of sodium. (b) Draw a labelled diagram of electrolytic refining of copper.

OR: What happens when (Write the balanced equation involved) - (i) Copper is heated in air? (ii) Aluminium oxide is reacted with hydrochloric acid? (iii) Potassium reacts with water? (iv) Cinnabar is heated in air? (v) Aluminium oxide reacts with sodium hydroxide?

(a) What is a homologous series? Explain with an example. (b) Define the following terms giving one example of each. (i) Esterification (ii) Addition reaction

(a) Describe the structure and function of the basic filtering unit of kidney. (b) List two factors on which reabsorption of water from urine depends?

(a) List three different categories of contraception methods. (b) Why has Government of India prohibited prenatal sex determination by law? State its benefits in the long run. (c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.

OR: (a) In the female reproductive system of human beings, state the functions of (i) ovary (ii) oviduct (b) Mention the changes which the uterus undergoes, when (i) it has to receive a zygote. (ii) no fertilization takes place. (c) State the function of placenta.

(a) Find the ratio of resistances of two copper rods X and Y of lengths 30 cm and 10 cm respectively and having radii 2 cm and 1 cm respectively. (b) A current of 500 mA flows in a series circuit containing an electric lamp and a conductor of 10Ω when connected to 6V battery. Find the resistance of the electric lamp.

(a) A concave mirror of focal length 10 cm can produce a magnified real as well as virtual image of an object placed in front of it. Draw ray diagrams to justify this statement. (b) An object is placed perpendicular to the principal axis of a convex mirror of focal length 10 cm. The distance of the object from the pole of the mirror is 10 cm. Find the position of the image formed.

OR: (a) Define the following terms: (i) Power of a lens (ii) Principal focus of a concave mirror (b) Write the relationship among the object distance (u), image distance (v) and the focal length (f) of a (i) Spherical lens (ii) Spherical mirror (c) An object is placed at a distance of 10 cm from optical centre of a convex lens of focal length 15 cm. Draw a labelled ray diagram to show the formation of image in this case.