Solution of Chapter (NCERT - Exemplar Science Book)

Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by liberation of heat. This process is called slaking of lime. Which among the following is (are) true about slaking of lime?

(i) It is an endothermic reaction

(ii) It is an exothermic reaction

(iii) The pH of the resulting solution will be more than seven

(iv) The pH of the resulting solution will be less than seven

Sodium carbonate is a basic salt because it is a salt of

Which one of the following four metals would be displaced from the solution of its salt by other three metals?

Which one among the following is the correct representation of electron dot structure of nitrogen

The correct sequence of anaerobic reactions in yeast is

Offspring formed as a result of sexual reproduction exhibit more variations because

New species may be formed if

(i) DNA undergoes significant changes in germ cells

(ii) chromosome number changes in the gamete

(iii) chromosome number remains the same

(iv) mating does not take place

Beams of light are incident through the holes A and B and emerge out of the box through the holes C and D respectively as shown in the Figure. Which of the following could be inside the box?

The clear sky appears blue because

Identify the given circuit in which the electrical components have been properly connected.

The resistance between A and B in the given Figure will be

In the arrangement shown in given Figure, there are two coils wound on a non-conducting cylindrical rod. Initially the key is not inserted. Then the key is inserted and later removed. Then

A constant current flows in a horizontal wire in the plane of the paper from east to west as shown in the given Figure. The direction of magnetic field at a point will be North to South

The major problem in harnessing nuclear energy is how to

Which of the statements is incorrect?

Write the balanced chemical equations for the following reactions and identify the type of reaction in each case:

(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.

(b) Limestone is heated strongly to form quicklime and carbon dioxide gas is evolved

Salt A commonly used in bakery products on heating converts into another salt B which is used in the manufacture of glass and a gas C is evolved. The gas C when passed through lime water, turns it milky. Identify A, B and C. Write the reaction for heating of salt A.

Properties of the elements are given below. Where would you locate the following elements in the Periodic Table?

(a) A soft metal stored under kerosene

(b) An element with variable (more than one) valency stored under water.

Why is ‘nutrition’ a necessity for an organism?

Why is the flow of signals in a synapse from axonal end of one neuron to dendritic end of another neuron but not the reverse?

In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.

Sudha finds out that the sharp image of the window pane of her science laboratory is formed at a distance of 15 cm from the lens. She now tries to focus the building visible to her outside the window instead of the window pane without disturbing the lens. In which direction will she move the screen to obtain a sharp image of the building? What is the approximate focal length of this lens?

A student sitting at the back of the classroom cannot read clearly the letters written on the blackboard. What advice will a doctor give to her? Draw ray diagram for the correction of this defect.

How will you use two identical prisms so that a ray of white light incident on one prism emerges out of the second prism as white light? Draw the diagram.

Three 60 W incandescent bulbs are connected in a parallel.

(a) Calculate the total power consumed.

(b) Now suppose that one of the bulbs is fused. What will be the total power consumed now?

A magnetic compass shows a deflection when placed near a current carrying wire. How will the deflection of the compass get affected if the current in the wire is increased? Support your answer with a reason.

What is the difference between the direct and alternating currents? How many times does AC used in India change direction in one second?

What steps would you suggest to minimise environmental pollution caused by burning of fossil fuels?

List the common food chain of a pond ecosystem

List two advantages associated with water harvesting at the community level.

Explain the following

(a) The reactivity of a piece of aluminium metal decreases if it is dipped in HNO₃

(b) Carbon cannot reduce the oxides of Na or Mg

(c) NaCl does not conduct electricity in solid state whereas it does conduct electricity in aqueous solution as well as in molten state

(d) Necessity of galvanisation of iron articles

(e) Metals like Na, K, Ca and Mg are never found in their free state in nature.

OR

Given below are the steps for extraction of copper from its ore.

(a) Write the equations of the reactions involved in roasting of copper (I) sulphide followed by its reduction.

(b) Draw a neat labelled diagram for electrolytic refining

You are given the balls and sticks models of six carbon atoms and fourteen hydrogen atoms and sufficient number of sticks. In how many ways one can join the models of six carbon atoms and fourteen hydrogen atoms to form different molecules of C₆H₁₄.

OR

Draw structural formulae of all the possible isomers of the compound with molecular formula C₃H₆O and also give their electron dot structures.

Distinguish between pollination and fertilisation. Mention the site and product of fertilisation in a flower. Draw a neat, labelled diagram of a pistil showing pollen tube growth and its entry into the ovule.

OR

Reproduction is essentially a phenomenon that is not for survival of an individual but for continuation of a species. Justify

(a) Draw ray diagrams showing the image formation by a convex lens when an object is placed

(i) at twice the focal length of the lens

(ii) at infinity

(b) The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. If the image is three times the size of the flame and the distance between lens and image is 80 cm, at what distance has the candle been placed from the lens? What is the nature of the image and the lens?

OR

Write laws of refraction of light. Explain the same with the help of ray diagram, when a ray of light passes through a rectangular glass slab

How will you infer with the help of an experiment that the same current flows through every part of the circuit containing three resistances in series connected to a battery?

OR

Find out the following in the electric circuit given in the Figure.

(a) Effective resistance of two 8 Ω resistors in combination.

(b) Current flowing through 4 Ω resistor.

(c) Potential difference across 4 Ω resistor.

(d) Power dissipated by 4 Ω resistor.

(e) Difference in ammeter readings, if any.

In the context of conservation of natural resources, explain the terms reduce, recycle and reuse. From among the materials that we use in daily life, identify two materials for each category.

OR

Suggest a few useful ways of utilising waste water.

Which among the following statement(s) is(are) true? Silver chloride on exposure to sunlight for long duration turns grey due to

(i) the formation of silver by decomposition of silver chloride

(ii) sublimation of silver chloride

(iii) decomposition of chlorine gas from silver chloride

(iv) oxidation of silver chloride

Which of the following oxide(s) of iron would be obtained on prolonged reaction of iron with steam?

Which of the following gives the correct increasing order of the atomic radii of O, F and N?

Which of the following statement(s) is(are) true about heart?

(i) Left atrium receives oxygenated blood from different parts of the body while right atrium receives deoxygenated blood from lungs

(ii) Left ventricle pumps oxygenated blood to different body parts while right ventricle pumps deoxygenated blood to lungs

(iii) Left atrium transfers oxygenated blood to right ventricle which sends it to different parts of the body

(iv) Right atrium receives deoxygenated blood from different parts of the body while left ventricle pumps oxygenated blood to different parts of the body

The substance that triggers the fall of mature leaves and fruits from plants is

Which among the following statements are true for unisexual flowers?

(i) They possess both stamen and pistil

(ii) They possess either stamen or pistil

(iii) They exhibit cross pollination

(iv) Unisexual flowers possessing only stamens cannot produce fruits

According to the evolutionary theory, formation of a new species is generally due to

Under which of the following conditions the real image formed by a concave mirror is larger than the actual object?

The path of a ray of light passing through a rectangular glass slab tested by four students are shown in Figure as A, B, C and D. Which one of them is correct?

In the following given circuits, heat produced in the resistor or combination of resistors connected to a 12 V battery will be

What is the maximum resistance which can be made using five resistors each of 1/5 Ω?

In an electrical circuit three incandescent bulbs A, B and C of rating 40 W, 60 W and 100 W are connected in parallel to an electric source. Which of the following is likely to happen regarding their brightness?

Choose the incorrect statement

Among the statements given below select the ones that describe the concept of sustainable development

(i) Planned growth with minimum damage to the environment

(ii) Growth irrespective of the extent of damage caused to the environment

(iii) Stopping all developmental work to conserve the environment

(iv) Growth that is acceptable to all the stakeholders

Identify the oxidising agent (oxidant) in the following reactions

(a) Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O

(b) Mg + 2H₂O → Mg (OH)₂ + H₂

(c) CuSO₄ + Zn → Cu + ZnSO₄

(d) V₂O₅ + 5Ca → 2V + 5CaO

A non-metal A is an important constituent of our food and forms two oxides B and C. Oxide B is toxic whereas C causes global warming

(a) Identify A, B and C

(b) To which Group of periodic table A belongs?

Atomic number of a few elements are given below

(i) 10 (ii) 20

(iii) 7 (iv) 14

(a) Identify the elements

(b) Identify the period to which these elements belong

What will happen if the mucus is not secreted by the gastric glands?

Name the plant hormones responsible for the following

(a) elongation of cells

(b) growth of stem

(c) promotion of cell division

(d) falling of senescent leaves

How are general growth and sexual maturation different from each other?

A very small population of a species faces a greater threat of extinction. Provide a suitable genetic explanation.

It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) positively charged alpha particles, (ii) neutrons? Justify your answer by giving suitable arguments.

A child has drawn the electric circuit to study Ohm’s law as shown in the figure. His teacher told that the circuit diagram needs correction.

Three 2 Ω resistors, A, B, and C, are connected as shown below. Each of them dissipates and can stand a maximum power of 18 W without melting. Find the maximum current that can flow through the three resistors.

Draw the reflected ray corresponding to the ray incident on a concave mirror as shown in the ray diagram?

Why does a light ray incident on a rectangular glass slab immersed in any medium emerge parallel to itself? Explain using a diagram.

A person needs a lens of power –4.5 D for correction of her vision.

(a) What kind of defect in vision is she suffering from?

(b) What is the focal length of the corrective lens?

(c) What is the nature of the corrective lens?

In a village in Karnataka, people started cultivating crops all around a lake which was always filled with water. They added fertilisers to their field in order to enhance the yield. Soon they discovered that the waterbody was completely covered with green floating plants and fish in the lake started dying in large numbers. Analyse the situation and give reasons for excessive growth of plants and death of fishes in the lake.

Although coal and petroleum are produced by degradatioin of bio- mass, yet we need to conserve them. Why?

In the following schematic diagram for the preparation of hydrogen gas as shown in Figure, what would happen if following changes are made?

(a) In place of Zn granules , same amount of zinc dust is taken in the test tube

(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken

(c) In place of Zn, Cu turnings are taken

(d) Sodium hydroxide is taken in place of sulphuric acid and tube is heated

OR

A metal carbonate X on reacting with an acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at anode during electrolysis of brine is passed on dry Y, it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G and Z. Also, write the chemical reactions involved.

When ethanoic acid reacts with sodium hydrogencarbonate, a salt X is formed and a gas Y is evolved.

(a) Identify X and Y. Write chemical equation of reaction involved.

(b) Describe an activity and draw the diagram of the apparatus to prove that the evolved gas is the one which you have named.

OR

Look at Figure and answer the following questions.

(a) What change would you observe in tube B containing calcium hydroxide solution

(b) Write the reaction involved in test tubes A and B respectively

(c) If ethanol is given instead of acetic acid, would you expect the same change?

(d) How can a solution of lime water be prepared in the laboratory?

When do we consider a person to be myopic or hypermetropic? Explain using diagrams how the defects associated with myopic and hypermetropic eye can be corrected?

OR

Explain the refraction of light through a triangular glass prism using a labelled ray diagram. Hence define the angle of deviation.

How can solar energy be harnessed? What are the limitations in using solar energy? How are these limitations overcome?

OR

What is biomass? Explain the principle and working of a biogas plant using a labelled schematic diagram

Explain with the help of a labelled diagram the distribution of a magnetic field due to a current through a circular loop. Why is it that if a current carrying loop has n turns the field produced at any point is n times as large as that produced by a single turn?

OR

Explain the phenomenon of electromagnetic induction? Describe an appropriate experiment to show that a current is set up in a closed loop when an external magnetic field passing through the loop increases or decreases.

Suggest any five activities in daily life which are eco-friendly.

OR

Explain some harmful effects of agricultural practices on the environment.