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CBSE Class 10 Science Solved Question Paper 2016

Long Answer Type

31.
a) Give a chemical test to distinguish between saturated and unsaturated hydrocarbon.

b) Name the products formed when ethane burns in the air. Write a balanced chemical equation for the reaction showing the types of energies liberated.

c) Why is the reaction between methane and chlorine in the presence of sunlight considered a substitution reaction?

A chemical test to distinguish between saturated and unsaturated hydrocarbon.

Bromine water test - Unsaturated hydrocarbon gives addition reaction with Br₂. So the colour of Br₂-water gets decolourized.

R-C=C=R + Br₂ --> R-BrC-CBr-R
whereas,
Saturated hydrocarbons do not react with Br₂-water so the colour of Br₂ -water does not get decolourised.

b) when ethane (CH₃-CH₃) is Burned in air (oxygen), it forms carbon dioxide and water.

CH₃-CH₃ +7/2O₂ --> 2CO₂ +3H₂O + Heat

This reaction is called an exothermic reaction due to the evolution of heat.

c) when methane reacts with chlorine in the presence of light, the following reaction takes place:
$CH subscript 4 space plus Cl subscript 2 space rightwards arrow with Sun space light on top space CH subscript 3 Cl space plus HCl$
It is considered a substitution reaction because in this reaction hydrogen is substituted with chlorine.

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32.

(a) Define the following terms in the context of spherical mirrors:

i) Pole

ii) Centre of curvature

iii) Principal axis

iv) Principal focus

b) Draw ray diagrams to show the principal focus of a

i) concave mirror
ii) convex mirror

c) Consider the following diagram in which M is a mirror and P is an object and Q is its magnified image formed by the mirror.

State the type of mirror and one characteristic property of the image Q.

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33. (a) Draw a ray diagram to show the formation of an image by a convex lens when an object is placed in front of the lens between its optical centre and principal focus.

(b) In the above ray diagram, mark the object distance (u) and the image distance (v) with their proper signs (+ve or –ve as per the new Cartesian sign convention) and state how these distances are related to the focal length (f) of the convex lens in this case.

(c) Find the power of a convex lens which forms a real and inverted image of magnification –1 of an object placed at a distance of 20 cm from its optical centre.

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34. (a) Write the function of each of the following parts of the human eye:

Cornea; iris; crystalline lens; ciliary muscles

(b) Millions of people in the developing countries of the world are suffering from corneal blindness. These persons can be cured by replacing the defective cornea with the cornea of a donated eye. A charitable society of your city has organised a campaign in your neighbourhood in order to create awareness about this fact. If you are asked to participate in this mission, how would you contribute in this noble cause?

(i) State the objective of organising such campaigns.

(ii) List two arguments which you would give to motivate the people to donate their eyes after death.

(iii) List two values which are developed in the persons who actively participate and contribute in such programmes.

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35.

(a) Write the functions of the following parts in human female reproductive system:

(i) Ovary
(ii) Oviduct
(iii) Uterus

(b) Describe the structure and function of placenta.

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36.

What is meant by speciation? List four factors that could lead to speciation. Which of them cannot be a major factor in the speciation of a self pollinating plant species. Give reason to justify your answer.

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