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Name two metals which are the best conductors of heat.

Silver and Copper are the best conductors of heat. Most conducting materials used for practical applications are metals.This is because metals... View Article

Write two properties of gold which make it the most suitable metal for ornaments.

Gold is a soft bright, dense, soft, malleable, and ductile metal with a slightly reddish yellow color when available in mass. But when divided... View Article

Define water of crystallisation. Give the chemical formula for two compounds as examples. How can it be proved that the water of crystallisation makes a difference in the state and colour of the compounds?

Water of crystallization is the fixed number of water molecules present in one formula unit of a salt. Examples: CuSO4.5H2O - Blue vitriol... View Article

A cloth strip dipped in onion juice is used for testing a liquid ‘X’. The liquid ‘X’ changes its odour. Which type of an indicator is onion juice? The liquid ‘X’ turns blue litmus red. List the observations the liquid ‘X’ will show on reacting with the following: (a) Zinc granules (b) Solid sodium carbonate Write the chemical equations for the reactions involved.

Onion juice is an olfactory indicator. As liquid X turns blue litmus red. Hence, it is a acid. (a) Zinc granules: Zinc granules react with acids... View Article

A person may suffer from both myopia and hypermetropia defects. (a) What is this condition called? (b) When does it happen? (c) Name the type of lens often required by the persons suffering from this defect. Draw labelled diagram of such lenses.

(a) This condition is called Presbyopia. (b) This defect occurs in old age due to the gradual weakening of the ciliary muscle and the eye-lens... View Article

The refractive index of a medium ‘x’ with respect to a medium ‘y’ is 2/3 and the refractive index of medium ‘y’ with respect to medium ‘z’ is 4/3. Find the refractive index of medium ‘z’ with respect to medium ‘x’. If the speed of light in medium ‘x’ is 3 * 10^8 ms^-1, calculate the speed of light in medium ‘y’.

The refractive index of medium 'x' with respect to medium 'y', nxy,or nx/ny = 2/3 The refractive index of medium 'y' with respect to... View Article

A concave mirror is used for image formation for different positions of an object. What inferences can be drawn about the following when an object is placed at a distance of 10 cm from the pole of a concave mirror of focal length 15 cm? (a) Position of the image (b) Size of the image (c) Nature of the image Draw a labelled ray diagram to justify your inferences.

Object distance, u = −10 cm(object distance will be negative, as it is placed on the left side of the mirror) Focal length, f = −15 cm(focal... View Article

‘‘During the course of evolution, organs or features may be adapted for new functions.’’ Explain this fact by choosing an appropriate example.

‘During the course of evolution, organs or features may be adapted for new functions. For example, Feathers were developed form providing... View Article

Define the term evolution. ‘‘Evolution cannot be equated with progress.’’ Justify this statement.

Evolution is defined as a process of gradual changes which takes in primary organisms over millions of years in which new species are... View Article

Define geotropism. Draw a labelled diagram of a plant showing geotropic movements of its parts.

Geotropism is the movement or growth of plant parts in response to the force of gravity. Just like phototropism, geotropism is also caused by an... View Article

A cheetah, on seeing a prey, moves towards him at a very high speed. What causes the movement of his muscles? How does the chemistry of cellular components of muscles change during this event?

As cheetah moves towards prey at a very high speed, several chemical changes occur at the cellular level of muscles such as adrenaline secretion... View Article

Carbon, a member of group 14, forms a large number of carbon compounds estimated to be about three million. Why is this property not exhibited by other elements of this group? Explain.

In group 14, carbon atom has smallest size. This enables the nucleus to hold on to the shared pairs of electrons strongly but the bonds formed by... View Article

Compare in tabular form the reactivities of the following metals with cold and hot water: (a) Sodium (b) Calcium (c) Magnesium

Sodium Calcium Magnesium 2Na + 2H2O → 2NaOH + H2 +Heat 2Ca + 2H2O → 2Ca(OH)2 + H2 Mg + 2H2O→Mg(OH)2 + H2 The... View Article

List three differentiating features between the processes of galvanisation and alloying.

Galvanization Alloying Galvanization or galvanizing (also spelled galvanisation or galvanising) is the process of applying a protective zinc... View Article

What happens when food materials containing fats and oils are left for a long time? List two observable changes and suggest three ways by which this phenomenon can be prevented.

When food materials containing fats and oils are left for a long time they become rancid. Rancidification is the process of complete or... View Article

Lead nitrate solution is added to a test tube containing potassium iodide solution. (a) Write the name and colour of the compound precipitated. (b) Write the balanced chemical equation for the reaction involved. (c) Name the type of this reaction justifying your answer.

(a) The name of the compound precipitated is Lead iodide. It is yellow in colour. (b) The balanced chemical equation for the reaction involved... View Article

Assertion (A): The sex of a child in human beings will be determined by the type of chromosome he/she inherits from the father. Reason (R): A child who inherits ‘X’ chromosome from his father would be a girl (XX), while a child who inherits a ‘Y’ chromosome from the father would be a boy (XY). (a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A). (b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A). (c) (A) is true, but (R) is false. (d) (A) is false, but (R) is true.

The given assertion and reason both are true. Also R is correct explanation of A. Humans have 23 pairs of chromosomes. Out of these 23 pairs,... View Article

Assertion (A): Following is a balanced chemical equation for the action of steam on iron: 3Fe + 4H2O —-> Fe3O4 + 4H2 Reason (R): The law of conservation of mass holds good for a chemical equation. (a) Both (A) and (R) are true and (R) is the correct explanation of the assertion (A). (b) Both (A) and (R) are true, but (R) is not the correct explanation of the assertion (A). (c) (A) is true, but (R) is false. (d) (A) is false, but (R) is true.

a) The given assertion and reason both are true. Also R is correct explanation of A. The Assertion given is : Following is a balanced chemical... View Article

Choose the incorrect statement from the following: (A) Ozone is a molecule formed by three atoms of oxygen. (B) Ozone shields the surface of the Earth from ultraviolet radiations. (C) Ozone is deadly poisonous. (D) Ozone gets decomposed by UV radiations.

(D) Ozone gets decomposed by UV radiations. Ozone is the chained molecule, harmful reactive gas and composed of three oxygen atoms that protect... View Article

Food web is constituted by (A) relationship between the organisms and the environment. (B) relationship between plants and animals. (C) various interlinked food chains in an ecosystem. (D) relationship between animals and environment.

(C) various interlinked food chains in an ecosystem. There are different types of food webs which are: Source web - one or more nodes, all of... View Article

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