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Page No 365:

Question 1:

Two solutions A and B have pH values of 4 and 10, respectively. Which solution has more hydrogen ion concentration?


Solutions having higher hydrogen ion concentration will be more acidic. So, the solution "A"  is more acidic as it has a lower pH.

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Question 2:

A potted plant is made to lie horizontally on the ground. Which part of the plant will show
(i) positive geotropism    (ii) negative geotropism?


 (i) Positive geotropism - roots
(ii) Negative geotropism - shoots

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Question 3:

Give one example each of characters that are inherited and the ones that are acquired in humans. Mention the difference between the inherited and the acquired characters.


Eye colour or hair colour of a human being is an example of inherited character whereas body weight is an example of acquired character.

The basic difference between inherited and acquired characters is that inherited characters are passed on from parent to offspring. On the other hand, acquired characters are acquired by an individual during his/her lifetime depending upon his/her lifestyle.

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Question 4:

What is a redox reaction? When a magnesium ribbon burns in air with a dazzling flame and forms a white ash, is magnesium oxidised or reduced? Why?


Redox reactions are those reactions in which simultaneous oxidation and reduction of chemical species are involved. In a redox reaction, one specie is reduced and another is oxidized.

Magnesium and oxygen combine to form magnesium oxide,

Since magnesium gains oxygen, we can say that it gets oxidized.

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Question 5:

What is a solar cell panel? State its two main advantages.


A solar cell panel is a device to convert light energy from the sun into electrical energy. Two advantages of solar cell panels are as follows:

(i) Solar cell panels are eco-friendly. They use the sun's light energy, which is unlimited and a natural source.

(ii) They are very easy to operate compared to other power sources of renewable type.

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Question 6:

What type of chemical reaction is represented by the following chemical equation? What does it tell us about the relative chemical reactivities of iron and aluminium?
Fe2O3 + 2Al → Al2O3 + 2Fe
State one use of the above chemical reaction.


Following chemical reaction an example of displacement reaction and redox reaction.

Fe2O3 + 2Al → Al2O3 + 2Fe

As aluminium is more reactive than iron it will displace iron from iron oxide and forms aluminium oxide. 
Iron loses oxygen and aluminium gains oxygen, so iron is reduced and aluminum is oxidized.

Since it is a highly exothermic reaction, it is used for welding purposes.

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Question 7:

What is a chemical equation? Why are chemical equations balanced? Write a balanced chemical equation with state symbols for the following reaction:
Solutions of barium chloride and sodium sulphate in water react to give insoluble barium sulphate and the solution of sodium chloride.


A chemical equation is a symbolic representation of the process that occurs in a chemical reaction. A chemical equation is written with the reactants on the left side of an arrow and the products of the chemical reaction on the right side of the equation.
The law of conservation of mass states that mass can neither be created nor be destroyed. Hence, in a chemical reaction, the total mass of the reactants should be equal to the total mass of the products.
Balanced chemical equation: BaCl2(aq)+Na2SO4(aq)2NaCl(aq)+BaSO4(s)

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Question 8:

The atom of an element has electronic configuration 2, 8, 8, 2.
(a) What is the atomic number of the element?
(b) To which of the following elements would it be chemically similar? (Atomic numbers of elements are given in brackets)
      He (2); O (8); Mg (12); K (19)
​Give reason for your choice.


(a) The atomic number of an element will be 20.

(b) Electronic configuration of the element is 2, 8, 8, 2. So, from this, we can conclude that it belongs to the second group of the periodic table. In modern periodic table elements with similar properties are placed in the same group. Out of the given options magnesium belongs to the same group as the electronic configuration of magnesium is 2, 8, 2.

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Question 9:

(a) What is the general formula of alkenes? Identify the alkenes from the following:
      C2H6, C2H4, C3H4, C2H2, C3H6
(b) Which of the following can give addition reactions?
      C2H6, C3H8, C3H6, C2H2, CH4
​Give reason for your choice.


(a) The general formula for alkenes is CnH2n
Out of given options C2H4, C3Hare alkenes.

(b) Addition reactions are generally shown by unsaturated molecules i.e. molecules having a double or triple bond. 
So, out of given options C3H6, C2Hwill give an addition reaction.


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Question 10:

(a) What is meant by short-circuiting in electric supply?
(b) What is the function of earth wire in electrical instruments?
(c) What is the usual current rating of the fuse wire in the power supply line which runs
​(i) lights and fans, and (ii) appliances of 2 kW power?


(a) When the live wire comes in contact with the neutral wire, the electric supply is said to be short-circuited. Due to short-circuiting in electric supply, a high amount of current flows in the circuit, which may damage various electric appliances or even start a fire.

(b) The function of the earth wire in the electrical instruments is to provide an immediate path to excess or unnecessary current in the circuit into the ground. It reduces the chances of getting a shock.

(c) (i) The usual current rating of the fuse wire in the line which runs lights and fans is 5 A.
(ii)The usual current rating of the fuse wire in the line which runs appliances of 2kW or more power is 15 A.

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Question 11:

(a) What type of lens is used as a magnifying glass?
(b) What type of lens is used to correct the defect of vision called myopia?
​(c) A convex lens has a focal length of 10.5 cm. Where should an object be placed in front of this convex lens so as to obtain an image which is real, inverted and same size as the object?


(a) A convex lens that is used to produce a magnified image of an object in a magnifying glass (called a hand lens in laboratory contexts).

(b) A concave lens (minus powered) is used to correct the defect of a myopic eye. 

(c) A convex lens forms a real image of the same size and inverted in nature when the object is placed at point '2f' of the convex lens. 

The focal length of the given lens = 10.5 cm

Hence, the object should be placed 21 cm away from the pole to form the required image.


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Question 12:

What is spectrum? Draw a labelled diagram to show the formation of the spectrum. Name the various colors of the spectrum.


A spectrum is a band of colors. It is produced when component colors of light are separated at different degrees by refraction through a prism. A spectrum of light is shown in the diagram given below:

There are mainly seven colors present in the spectrum of light. i.e. Violet, Indigo, Blue, Green, Yellow, Orange, and Red.

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Question 13:

(a) How does the embryo get nourishment inside the mother's body?
​(b) If the blood group of father is A and the blood group of mother is O, what will be the blood group of their daughter? Explain how you have arrived at your answer.


(a) An embryo gets nourishment inside the mother's body through placenta. It is a special disc-like organ that develops in the fourth week of pregnancy. It establishes an intimate connection between the foetal membrane and the uterine wall via umbilical cord.

Function of Placenta:

  • The exchange of materials between the blood of mother and foetus takes place through placenta.
  • It provides nutrition to the foetus.
  • It also serves as the respiratory (by allowing exchange of oxygen and carbon dioxide) and excretory organ (by allowing excretion of waste material of foetus into mother's blood) of the foetus.

(b) The blood group of mother is O which means, it has the genotype ii.
The blood group of father is A which means, he can have the genotype IAIA or IAi.

Case I - If the genotype of father's blood group is IAIA and mothers is ii.

In this case, the daughter will have the blood group A.

If the genotype of father's blood group is IAi and mothers is ii


In this case, the daughter has 50% chances of having blood group A and 50% chances of having blood group O.

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Question 14:

What is meant by "speciation"? State the various factors which could lead to the formation of new species.


The formation of a new species by evolution or any genetic modification of the previously existing species in a population is called speciation.

Following are the factors responsible for speciation:
1. Genetic drift - The accidental change in the frequency of genes in a small population is called genetic drift.
2. Natural selection - It is a process that results in an increased survival and reproductive success of individuals that are well adjusted to the environment.
3. Reproductive isolation - It refers to the absence of other reproductively compatible plants in the same area.
4. Geographical isolation - It refers to a type of barrier which prevents the mating between members of a species due to geographical barriers.

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Question 15:

(a) In the human body, what is the role of (i) seminal vesicles, and (ii) prostrate gland?
​(b) List two functions performed by testes in human beings.


(a) (i) Seminal vesicles - The secretions of seminal vesicles contain many proteins and enzymes and thus provide nutrition to the developing sperms.

(ii) Prostate gland - The prostate gland secretes a slightly alkaline fluid that lubricates the sperms and neutralises the acidity of the vaginal tract.

(b) Two important functions of testes are -

(i) Production of sperms

(ii) Production of a hormone called testosterone, which brings about secondary sexual characters in boys

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Question 16:

(a) Give the electronic configurations of sodium and chlorine.
(b) Write the electron-dot structures for sodium and chlorine atoms.
(c) Describe the formation of sodium chloride from sodium and chlorine by the transfer of electrons. What changes take place in the electronic configurations of sodium and chlorine during the formation of sodium chloride?
​(d) Write any two properties of ionic compounds.


(a) Electronic configuration of sodium = 2, 8, 1
Electronic configuration of chlorine = 2, 8, 7



Sodium will lose one electron and become electron deficient while chlorine gains one electron and becomes electron rich.

(d) Properties of ionic compound:
(i) They are hard because of the strong force of attraction between positive and negative ions.
(ii) They have high melting and boiling point.
(iii) They are generally soluble in water but insoluble in inorganic solvents.


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Question 17:

(a) Name two metals which are found in free state in nature.
(b) What chemical process is used for extracting a metal from its oxide ore? Name one metal which is extracted by this method.
​(c) Describe the extraction of zinc metal from its sulphide ore as well as its carbonate ore. Write equations of all the reactions involved.


(a) Metals in the bottom of the reactivity series are found in the free state. For eg. gold, platinum, silver, etc.

(b) Metal can be extracted from its oxide ore by electrolytic reduction. Aluminium metal can be extracted by electrolytic reduction of molten aluminium oxide.


(c) Zinc is extracted from its carbonate ore by calcination process in which carbonate ore is heated strongly in the absence of air to convert it into zinc oxide.

ZnCO3(s)zinc carbonate orecalcinationZnO(s)+CO2(g)

Zinc sulphide is extracted from its sulphide ore by roasting process in which sulphide ore is heated strongly in the presence of air to convert it into zinc oxide.

2ZnS(s)zinc sulphide+3O2(g)roasting2ZnO(s)+2SO2(g)

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Question 18:

(a) Name one device which works on the magnetic effect of current.
(b) Name one device which works on the phenomenon of electromagnetic induction.
(c) Which device converts electric energy into mechanical energy?
(d) Describe the principle of working of an electric motor.
​(e) Explain the principle of working of an electric generator.


(a) An electric motor works on the magnetic effect of current. 

(b) An electric generator works on the phenomenon of electromagnetic induction.

(c) An electric motor converts electrical energy into mechanical energy.

(d) The electric motor works on the principle of Fleming's left-hand rule. It states that when an electric current is passed through a conductor placed in a magnetic field, it experiences a force in a direction perpendicular to the direction of both the electric field and magnetic field. That force moves the coil of the electric motor, and that's how electric energy is converted into mechanical energy in an electric motor. 

(e) An electric generator works on the principle based on Fleming's right-hand rule. Which states that when a coil of insulated copper wire is forced to rotate inside a magnetic field, then electric current is induced. That's how an electric generator converts mechanical energy into electrical energy. 

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Question 19:

(a) For which position of an object, a real, diminished image is formed by a convex lens?
(b) Two convex lenses A and B have focal lengths of 2.5 cm and 12.0 cm, respectively. Which lens has a greater power?
​(c) Describe with the help of a labelled ray-diagram, the formation of image when an object is placed in the front of a convex lens between  focus and optical centre. State any two characteristics of the image formed.


(a) When an object is placed beyond '2f' of a convex lens, the image formed is diminished and real in nature.

(b) Power of a lens is indirectly proportional to its focal length. i.e. P1f(in meter)

According to the above relation, the lens with a smaller focal length would have greater power. So, lens A has greater power.


Characteristics of the image formed above:

(i) Image is virtual
(ii) Image is erect
(iii) Image is enlarged


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Question 20:

(a) Which of the following belong to the same trophic level?
      Grass, Hawk, Rabbit, Frog, Deer
Give reason for your choice.
​(b) What is the difference between the food habits of organisms belonging to the first and third trophic levels. Give one example each of the organisms belonging to first and third trophic levels.


(a) Rabbit and deer belong to the same trophic level. Both are herbivores and occupy the second trophic level.

(b) First trophic level is occupied by plants whereas third trophic level is occupied by carnivores or secondary consumers.
Plants are autotrophic in nature i.e. they can produce their own food and thus are also called producers. Example: plants
Whereas organisms which occupy the secondary trophic levels are called consumers. These organisms are meat eaters and depend on other organisms for their food needs. Example: tiger

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Question 21:

What is ozone? How is ozone formed? How does ozone layer product us from the harmful effects in the environment? Write the full form of CFC. What harm can they do?


Ozone layer is a layer consisting of ozone molecules which acts as a protective layer for life on the earth. 

It protects the earth by absorbing harmful ultraviolet radiations of the sun. These radiations, if reach the earth’s surface, can cause skin cancer.

The ozone layer is continuously formed in the atmosphere because of the action of UV rays on molecular oxygen. The high-energy UV radiations break down O2 molecules present in upper layers of the atmosphere into nascent oxygen.

Then, this free oxygen atom combines with an oxygen molecule to form ozone.

CFC stands for chlorofloro carbon. 
The ozone layer is getting depleted by the action of chlorofluorocarbons (CFCs) used as coolant in refrigerators and perfumes. The CFCs are acted upon by UV rays in the stratosphere, liberating the Cl atoms, which act as catalysts to degrade ozone into molecular oxygen.

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Question 22:

Draw the following diagram in your answer-book and show the formation of an image with the help of suitable rays.

​What will be the size of image relative to the size of the object?


When an object is placed at the radius of curvature of a concave mirror, the image formed has the same size as that of the object.

Hence, in given the case, the size of the image would be the same as the size of the object.

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Question 23:

A student is performing an experiment with two triangular glass prisms. He places the first glass prism on its base. The second glass prism is placed upside down behind the first glass prism. When a beam of white light is allowed to fall on the first glass prism, then a patch of ordinary white light is obtained on a screen placed behind the second glass prism.
(a) Draw a ray diagram to show the above arrangement of two glass prisms and the light passing through them.
​(b) What is the function of (i) first prism, and (ii) second prism, in this arrangement?



(b) (i) The function of the first prism is to split the white light into seven colors.
(ii) The function of the second prism is to recombine them back into white light.

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Question 24:

Five solutions A, B, C, D and E have pH values of 5, 10, 2, 7 and 12 respectively. Which solution is:
(a) weakly alkaline?
(b) strongly alkaline?
(c) weakly acidic?
​(d) strongly acidic?


(a) Out of given solutions, "B" will be weakly alkaline. On the pH scale, the higher the value of pH stronger will be the base.

(b) Out of given solutions, "E" will be strongly alkaline. On the pH scale, the higher the value of pH stronger will be the base.

(c) Out of given solutions, "A" will be weakly acidic. On the pH scale, lower the value of pH stronger will be the acid.

(d) Out of given solutions, "C" will be strongly acidic. On the pH scale, lower the value of pH stronger will be the acid.

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Question 25:

In order to carry out the decomposition reaction of water, a student passes electric current from a battery through water containing a few drops of dilute sulphuric acid. In this process, two volume of gas X are collected in a test-tube inverted over cathode (negative electrode) whereas one volume of gas Y is collected in the test-tube inverted over anode (positive electrode).
(a) Why do we add a few drops of dilute sulphuric acid to water before passing electric current?
(b) Name the gas X.
(c) Name the gas Y.
​(d) What does this decomposition reaction tell us about the composition of water?


(a) Decomposition of water is a very slow process and addition of dilute sulphuric acid increases the rate of decomposition of water.


(b) Gas X is hydrogen, which will accumulate at the cathode, as positively charged hydrogen ions will move towards the negatively charged cathode electrode.

(c) Gas Y is oxygen, which will accumulate at the anode, as negatively charged oxygen ions will move towards the positively charged anode electrode.

(d) When electricity is passed in water, it splits water into two hydrogen ions and one oxygen ions.

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Question 26:

A student takes a potted plant growing in a transparent glass jar. This potted plant having straight stem and straight root is kept near the window in a dark room so that sunlight falls on it from the right side (through the window). After some days, it is found that the stem of plant bends towards the right side (from where the light is coming) but the root bends to the left side, away from the light.
(a) What term is used to indicate:
     (i) response of plant to sunlight?
     (ii) bending of stem of plant towards sunlight?
     (iii) bending of root of plant away from sunlight?
(b) Name the plant hormone which makes the plant respond to sunlight.


(a) (i) response of plant to sunlight - phototropism
     (ii) bending of stem of plant towards sunlight -  phototropism
     (iii) bending of root of plant away from sunlight - geotropism

(b) Auxin is the plant hormone which makes the plant respond to sunlight.

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Question 27:

A person gets cramps in the legs during marathon (a long distance race).
(a) Name the chemical whose accumulation in his leg muscles produces cramps.
(b) What type of respiration produces this chemical?
(c) How can the person get relief from cramps in muscles caused during marathon?


(a) The chemical whose accumulation in leg muscles produce cramps is called lactic acid.
(b) Lactic acid is a product of anaerobic respiration.
(c) The person can get relief by placing his legs in warm water for some time. This improves the circulation of blood and removes the accumulation of lactic acid.

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