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Solutions for Science, Class 10, CBSE
A student took Sodium Sulphate solution in a test tube and added Barium Chloride solution to it. He observed that an insoluble substance has formed. The colour and molecular formula of the insoluble substance is:
White, BaSO4
Reason — When sodium sulphate is reacted with barium chloride, a white ppt. of barium sulphate is produced.
Na2SO4 (aq) + BaCl2 (aq) ⟶ BaSO4 (s) + 2NaCl (aq)
Which of the following oxide(s) is/are soluble in water to form alkalis?
(i) Na2O
(ii) SO2
(iii) K2O
(iv) NO2
(i) and (iii)
Reason — Sodium oxide and potassium oxide dissolve in water to form alkalis.
Na2O + H2O ⟶ 2NaOH
K2O + H2O ⟶ 2KOH
Study the diagram given below and identify the gas formed in the reaction.
Hydrogen which while burning produces a popping sound.
Reason — When zinc reacts with sulphuric acid, it produces hydrogen gas and zinc sulphate.
Zn + H2SO4 ⟶ ZnSO4 + H2↑
Sodium reacts with water to form sodium hydroxide and hydrogen gas. The balanced equation which represents the above reaction is
2Na(s) + 2H2O(l) ⟶ 2NaOH(aq) + H2(g)
Reason — The balanced equation for the reaction between sodium and water to form sodium hydroxide and hydrogen gas is:
2Na(s) + 2H2O(l) ⟶ 2NaOH(aq) + H2(g)
Which of the options in the given table are correct?
Option | Natural Source | Acid Present |
---|---|---|
(i) | Orange | Oxalic acid |
(ii) | Sour milk | Lactic acid |
(iii) | Ant sting | Methanoic acid |
(iv) | Tamarind | Acetic acid |
(ii) and (iii)
Reason — Sour milk contains lactic acid and ant sting contains methanoic acid.
C6H12O6 (aq) + 6O2 (aq) ⟶ 6CO2 (aq) + 6H2O (l)
The above reaction is a/an
exothermic reaction
Reason — The name of the above reaction is respiration and it is an exothermic reaction. The glucose from food combines with oxygen in the cells of our body and provides energy as heat.
Which of the following statements about the reaction given below are correct?
MnO2 + 4HCl ⟶ MnCl2 + 2H2O + Cl2
(i) HCl is oxidized to Cl2
(ii) MnO2 is reduced to MnCl2
(iii) MnCl2 acts as an oxidizing agent
(iv) HCl acts as on oxidizing agent
(i) and (ii) only
Reason — The reaction is a redox reaction where, HCl is oxidized to Cl2 as it loses hydrogen whereas MnO2 is reduced to MnCl2 as it loses oxygen.
Select from the following the statement which is true for bases.
Bases turn pink when a drop of phenolphthalein is added to them.
Reason — Phenolphthalein is a pH indicator which turns pink when added to a basic solution.
Study the following table and choose the correct option:
S. No. | Salt | Parent Acid | Parent Base | Nature of Salt |
---|---|---|---|---|
(a) | Sodium Chloride | HCl | NaOH | Basic |
(b) | Sodium Carbonate | H2CO3 | NaOH | Neutral |
(c) | Sodium Sulphate | H2SO4 | NaOH | Acidic |
(d) | Sodium Acetate | CH3COOH | NaOH | Basic |
Sodium Acetate | CH3COOH | NaOH | Basic |
Reason — Sodium acetate made from acetic acid and sodium hydroxide is basic in nature.
It is important to balance the chemical equations to satisfy the law of conservation of mass. Which of the following statements of the law is incorrect?
The chemical composition of the reactants is the same before and after the reaction.
Reason — During the reaction, the chemical composition of the reactants change to form new products. Hence, this statement is incorrect.
Consider the following statements in connection with the functions of the blood vessels marked A and B in the diagram of a human heart as shown.
(i) Blood vessel A — It carries carbon dioxide rich blood from the lungs.
(ii) Blood vessel B — It carries oxygen rich blood from the lungs.
(iii) Blood vessel B — Left atrium relaxes as it receives blood from this blood vessel.
(iv) Blood vessel A — Right atrium has thick muscular wall as it has to pump blood to this blood vessel.
The correct statements are
(i), (ii) and (iii)
Reason— Blood vessel A is Pulmonary artery that takes deoxygenated blood to lungs and Blood vessel B is Pulmonary vein that takes oxygenated blood from lungs to left atrium.
In living organisms during respiration which of the following products are not formed if oxygen is not available?
Carbon dioxide + Water
Reason — Carbon dioxide + Water is formed during aerobic respiration in presence of oxygen.
The correct statements with reference to single celled organisms are:
(i) Complex substances are not broken down into simpler substances.
(ii) Simple diffusion is sufficient to meet the requirement of exchange of gases.
(iii) Specialised tissues perform different functions in the organism.
(iv) Entire surface of organism is in contact wih the environment for taking in food.
(ii) and (iv)
Reason — In unicellular organisms respiration occurs by simple diffusion and they have entire cell surface to take food.
Which one among the following is not removed as a waste product from the body of a plant?
Urea
Reason — Plants do not excrete urea. Urea is an animal waste product.
Which of the following statements are correct in reference to the role of A (shown in the given diagram) during a breathing cycle in human beings?
(i) It helps to decrease the residual volume of the air in lungs.
(ii) It flattens as we inhale.
(iii) It gets raised as we inhale.
(iv) It helps the chest cavity to become larger.
(ii) and (iv)
Reason — While breathing in, we lift our ribs and flatten our diaphragm, and the chest cavity becomes larger. Because of this, air is sucked into the lungs and fills the expanded alveoli.
Which one of the following conditions is true for the state of stomata of a green leaf shown in given diagram?
Large amount of water flows out from the guard cells.
Reason — Large amount of water flows out from the guard cells making the cells flaccid. This closes the stomata. The stomata opens again when guard cells become turgid by taking in water.
In which of the following is a concave mirror used?
A solar cooker
Reason — Large concave mirrors are used to concentrate sunlight to produce heat in solar cookers.
A student wants to obtain a magnified image of an object AB as on a screen. Which one of the following arrangements shows the correct position of AB for him/her to be successful?
1.
2.
3.
4.
Reason — When the object is kept between F and 2F, enlarged, real and inverted image is obtained on the screen.
The following diagram shows the use of an optical device to perform an experiment of light. As per the arrangement shown, the optical device is likely to be a;
Concave lens
Reason — As the rays are passing through the device so it should be a lens and as we can see that the rays are diverging, hence it is a concave lens.
A ray of light starting from the air passes through medium A of refractive index 1.50, enters medium B of refractive index 1.33 and finally enters medium C of refractive index 2.42. If this ray emerges out in the air from C, then for which of the following pairs of media the bending of light is least?
A-B
Reason — The bending of light is least when the refractive index change is least. When light is travelling from medium A to medium B, the change in refractive index is from 1.50 to 1.33 which is the least in this case. Hence, the bending of light is also the least for A-B.
Which of the following statements is not true for the scattering of light?
Scattering of light takes place as various colours of white light travel with different speeds in air.
Reason — Various colours of white light travel with same speed in vacuum/air.
For the diagram shown, according to the new cartesian sign convention the magnification of the image formed will have the following specifications :
Sign — Positive, Value — More than 1
Reason — When the object is kept between focus and the optical centre in a concave mirror, then the image formed is of larger size than object and the image is erect.
A ray of light is incident as shown. If A, B and C are three different transparent media, then which among the following options is true for the given diagram?
∠ 3 = ∠ 2
Reason — As the two normals are parallel to each other, so ∠ 2 = ∠ 3 as they form a pair of alternate angles. Hence, ∠ 3 = ∠ 2 is true for the given diagram.
In the diagram given below, X and Y are the end colours of the spectrum of white light. The colour of 'Y' represents the
Colour used to paint the danger signals.
Reason — We can observe from the image that the Y colour has deviated the least. Hence, Y is red colour or the colour used to paint the danger signals.
Which one of the following reactions is categorized as a thermal decomposition reaction?
CaCO3 (s) ⟶ CaO(s) + CO2 (g)
Reason — The decomposition of CaCO3 is carried out by heating hence the above reaction is a thermal decomposition reaction.
Consider the pH value of the following acidic samples :
S. No. | Sample | pH Value |
---|---|---|
1. | Lemon Juice | 2.2 |
2. | Gastric Juice | 1.2 |
3. | Vinegar | 3.76 |
4. | Dil. Acetic acid | 3.0 |
The decreasing order of their H+ ion concentration is
2 > 1 > 4 > 3
Reason — The number of H+ ion concentration determines the acidic strength of the sample. The pH and hydrogen ion concentration are inversely related i.e., as the value of pH increases, the H+ ion concentration decreases hence decreasing order of their H+ ion concentration is 2 > 1 > 4 > 3.
Study the experimental set-up shown in given figure and choose the correct option from the following:
P | Q | Change observed in calcium hydroxide solution |
---|---|---|
1.K2CO3 | Cl2 gas | No change |
2.KHCO3 | CO2 gas | No change |
3.KHCO3 | H2 gas | Turns milky |
4.K2CO3 | CO2 gas | Turns milky |
K2CO3 | CO2 gas | Turns milky |
Reason — The reaction between potassium carbonate and HCl gas produces carbon dioxide gas.
K2CO3 + 2HCl (dil.) ⟶ 2KCl + H2O + CO2
Calcium hydroxide reacts with carbon dioxide gas and forms calcium carbonate, which turns the solution milky.
Ca(OH)2 + CO2 ⟶ CaCO3 + H2O
Which one of the following structures correctly depicts the compound CaCl2?
Reason — The valency of calcium is +2 and that of chlorine is -1. Two chlorine anions and one calcium cation form an ionic bond and the chemical formula of calcium chloride is CaCl2.
The pair(s) which will show displacement reaction is/are
(i) NaCl solution and copper metal
(ii) AgNO3 solution and copper metal
(iii) Al2(SO4)3 solution and magnesium metal
(iv) ZnSO4 solution and iron metal
(ii) and (iii)
Reason — AgNO3 solution and copper metal will give displacement reaction where copper being more reactive than silver, displaces it from silver nitrate . Similarly, Al2(SO4)3 solution and magnesium metal will give displacement reaction where magnesium being more reactive than aluminium, displaces it from aluminium sulphate.
Which of the following salts do not have the water of crystallisation?
(i) Bleaching Powder
(ii) Plaster of Paris
(iii) Washing soda
(iv) Baking soda
(i) and (iv)
Reason — Bleaching Powder [CaOCl2] and baking soda [NaHCO3] do not have water of crystallization whereas plaster of Paris [CaSO4. H2O] and washing soda [Na2CO3.10H2O] have.
Assertion (A): Sodium hydrogen carbonate is used as an ingredient in antacids.
Reason (R): NaHCO3 is a mild non-corrosive basic salt.
Both A and R are true and R is the correct explanation of A.
Reason — Sodium hydrogen carbonate [NaHCO3] is used as an ingredient in antacids, as it is a mild non-corrosive basic salt and it neutralizes the excess acid produced in our stomach.
Assertion (A): Burning of Natural gas is an endothermic process.
Reason (R): Methane gas combines with oxygen to produce carbon dioxide and water.
A is false and R is true.
Reason — Burning of natural gas is an exothermic process and methane gas combines with oxygen to produce carbon dioxide and water.
CH4 + 2O2 ⟶ CO2 + 2H2O
Assertion (A): Nitrogen is an essential element for plant growth and is taken up by plants in the form of inorganic nitrates or nitrites.
Reason (R): The soil is the nearest and richest source of raw materials like Nitrogen, Phosphorus and other minerals for the plants.
Both A and R are true, and R is not the correct explanation of A.
Reason — Nitrogen is changed into its nitrate or nitrite form by bacterial action.
Assertion (A): Sun appears reddish at the time of Sunrise and Sunset.
Reason (R): Distance travelled by sunlight in the atmosphere is lesser during sunrise and sunset as compared to noon.
A is true and R is false.
Reason — During the sunrise and sunset, the sun is near the horizon and most of the blue light and shorter wavelengths are scattered away by the particles. Therefore, the light that reaches our eyes is of longer wavelength. This gives rise to the reddish appearance of the sun.
During sunrise and sunset, sun is at a farther distance while at noon sun is directly overhead. Hence, distance travelled by sunlight in the atmosphere is more during sunrise and sunset as compared to noon.
Assertion (A): Hydrochloric acid helps in the digestion of food in the stomach.
Reason (R): Hydrochloric acid creates an acidic medium to activate protein digesting enzymes.
Both A and R are true, and R is the correct explanation of A.
Reason — The hydrochloric acid creates an acidic medium which facilitates the action of the enzyme pepsin by activating it.
A student was asked to write a stepwise procedure to demonstrate that carbon dioxide is necessary for photosynthesis. He wrote the following steps. The wrongly worded step is:
Both potted plants are kept in sunlight after the starch test.
Reason — Starch test is done after they have been kept in sunlight to know whether photosynthesis occurred or not.
Respiratory structures of two different animals — a fish and a human being are as shown.
Observe (a) and (b) and select one characteristic that holds true for both of them.
Both have thin and moist surface for gaseous exchange.
Reason — Gills as well as alveoli have moist surface. Also, fishes have only two chambers to their hearts, and the blood is pumped to the gills, is oxygenated there, and passes directly to the rest of the body.
Observe the diagram of an activity given below. What does it help to conclude, when the person exhales into the test-tube?
Percentage of carbon dioxide is more in exhaled air.
Reason — Exhaling through the straw turns the lime water milky showing that percentage of carbon dioxide is more in exhaled air.
If a lens can converge the sun rays at a point 20 cm away from its optical centre, the power of this lens is –
+5D
Reason — Given,
Convex lens as converging rays.
Focal length (f) = 20 cm
P =
Substituting we get,
P = = +5D [positive sign as convex lens.]
The radius of curvature of a converging mirror is 30 cm. At what distance from the mirror should an object be placed so as to obtain a virtual image?
Between 0 cm and 15 cm
Reason — Given, concave mirror as it is a converging mirror.
R = 30 cm
We know, R = 2f
Substituting we get, 30 = 2 x f
f = = 15 cm
In a concave mirror, virtual image is obtained when the object is placed between focus and optical centre hence, object should be placed between 0 cm and 15 cm.
The length of small intestine in a deer is more as compared to the length of small intestine of a tiger. The reason for this is :
Type of food consumed
Reason — The length of the small intestine differs in various animals depending on the food they eat. Herbivores eating grass need a longer small intestine to allow the cellulose to be digested. Meat is easier to digest, hence carnivores like tigers have a shorter small intestine.
Identify the two components of phloem tissue that help in transportation of food in plants.
Sieve tubes & companion cells
Reason— The translocation of food and other substances takes place in the sieve tubes with the help of adjacent companion cells both in upward and downward directions.
A converging lens forms a three-times magnified image of an object, which can be taken on a screen. If the focal length of the lens is 30 cm, then the distance of the object from the lens is
–40 cm
Reason — Given, convex lens as converging lens
f = 30 cm
From formula,
m =
-3 = [-ve sign as real and inverted image is formed.]
v = -3u
Using formula,
= -
We get,
= -
= =
3u = -4 x 30
u = = -40 cm
Hence, distance of the object from the lens = -40 cm.
Which of the following statements is not true in reference to the diagram shown below?
Image formed is enlarged.
Reason — When object is placed at the centre of curvature (i.e. 2f), the image is formed at the same point and of same size as the object.
In the diagram shown below n1, n2 and n3 are refractive indices of the media 1, 2 and 3 respectively. Which one of the following is true in this case?
n3 > n1
Reason — According to the figure, the light ray bends towards the normal when it passes from medium 1 to medium 2 and then it bends further when it passes from medium 2 to 3. We know, ray of lights bends towards the normal when it passes from rarer to denser medium hence medium 3 is denser than medium 1 i.e., n3 > n1.
The refractive index of medium A is 1.5 and that of medium B is 1.33. If the speed of light in the air is 3 × 108 m/s, what is the speed of light in medium A and B respectively?
(a) 2 × 108 m/s and 1.33 × 108 m/s
(b) 1.33 × 108 m/s and 2 × 108 m/s
(c) 2.25 × 108 m/s and 2 × 108 m/s
(d) 2 × 108 m/s and 2.25 × 108 m/s
2 × 108 m/s and 2.25 × 108 m/s
Reason — We know,
refractive index of medium =
Substituting we get,
For medium A,
1.5 =
speed of light in medium A =
Hence, speed of light in medium A = 2 × 108 m/s
For medium B,
1.33 =
speed of light in medium B =
Hence, speed of light in medium B =2.25 × 108 m/s
An object of height 4 cm is kept at a distance of 30 cm from the pole of a diverging mirror. If the focal length of the mirror is 10 cm, the height of the image formed is
+1.0 cm
Reason — Given, convex mirror as diverging mirror.
focal length (f) = 10 cm
u = -30 cm
ho = 4 cm
v = ?
Using formula,
= +
We get,
= -
= +
= =
=
v = = 7.5
m = - =
Substituting we get,
- =
height of the image = = +1 cm
Hence, height of the image = +1 cm
50.0 mL of tap water was taken in a beaker. Hydrochloric acid was added drop by drop to water. The temperature and pH of the solution was noted. The following graph was obtained. Choose the correct statements related to this activity.
(i) The process of dissolving an acid in water is highly endothermic.
(ii) The pH of the solution increases rapidly on addition of acid.
(iii) The pH of the solution decreases rapidly on addition of acid.
(iv) The pH of tap water was around 7.0.
(iii) and (iv)
Reason — The pH of tap water was around 7.0 because tap water is a neutral solution. On addition of acid to water the heat energy is released hence the reaction is exothermic. The pH of the solution decreases rapidly from 3 to 1 with the addition of acid.
Out of the given metals, the one which needs to be stored under Kerosene is
R
Reason — R reacts vigorously and catches fire when kept in open, hence it needs to be stored in kerosene oil. Example : sodium and potassium
Out of the given metals, the metal Q is
Magnesium
Reason — The metal Q is magnesium as it reacts with hot water only and starts floating due to the bubbles of hydrogen gas sticking to the surface.
Metal which forms amphoteric oxides is
P
Reason — The metal P combines with oxygen to form an amphoteric metal oxide M2O3 which reacted with both acids and bases.
The increasing order of the reactivity of the four metals is;
S < P < Q < R
Reason — Based on the reactions of the above given metals with water, the increasing order of reactivity is S < P < Q < R .
Case II
The figure shown below represents a common type of dialysis called as Haemodialysis. It removes waste products from the blood such as excess salts, and urea which are insufficiently removed by the kidney in patients with kidney failure. During the procedure, the patient's blood is cleaned by filtration through a series of semi-permeable membrane before being returned to the blood of the patient. On the basis of this, answer the following questions:
The haemodialyzer has semi-permeable lining of tubes which help to:
In passing the waste products in the dialyzing solution.
Reason — It allows the waste to pass from blood to dialyzing solution.
Which one of the following is not a function of Artificial Kidney?
To reabsorb essential nutrient from the blood.
Reason — Reabsorption of nutrient occurs only in kidney.
The 'used dialysing' solution is rich in:
Urea and excess salts
Reason — The Urea and excess salts move into the the dialyzing solution from the blood.
Which part of the nephron in human kidney, serves the function of reabsorption of certain substances?
Tubules
Reason — Reabsorption occurs in Proximal convoluted tubule of nephron.
Case III
A compound microscope is an instrument that consists of two lenses L1 and L2. The lens L1 called objective forms a real, inverted and magnified image of the given object. This serves as the object for the second lens L2; the eyepiece. The eyepiece functions as a simple microscope or magnifier. It produces the final image, which is inverted with respect to the original object, enlarged and virtual.
What types of lenses must be L1 and L2?
Both convex
Reason — A compound microscope is made up of two convergent lens i.e., two convex lens.
What is the value and sign of magnification (according to the new Cartesian sign convention) of the image formed by L1?
Value = More than 1 and Sign = Negative
Reason — The image formed is magnified and inverted, hence the magnification is more than one and with negative sign.
What is the value and sign of (according to the new Cartesian sign convention) magnification of the image formed by L2?
Value = More than 1 and Sign = Negative
Reason — The image formed is magnified and inverted, hence the magnification is more than one and with negative sign.
If the power of the eyepiece (L2) is 5 diopters and it forms an image at a distance of 80 cm from its optical centre, at what distance should the object be?
16 cm
Reason — Given,
Power = +5D [convex lens has positive sign]
v = -80 cm.
u = ?
From formula,
P =
Substituting we get,
5 =
f = = 20 cm
Using formula,
= -
We get,
= -
= - -
= =
=
u = -16
Hence, distance of the object from the lens = 16 cm.