Oswal Practice Papers CBSE Class 10 Science Solutions (Practice Paper - 9)

Section-A

1. (b) Concave in nature

Explanation :

As rear view mirror is a concave mirror. It has wider field of coverage and gives a virtual, erect and diminished image of an object.

2. (b) Conservation of mass

Explanation :

The law of conservation of mass states that “mass can neither be created nor destroyed.” So, both sides of the chemical reactions have to be balanced to ensure that this law is followed and thus, the number of the reactant and the product molecules remains the same on both sides of the equation.

3. (b) Move towards the wire

Explanation :

$$\text{Force F} =\frac{\mu_{0}2i_{1}i_{2}}{4\pi r}\\\therefore\space \text{F}\propto\frac{1}{r}$$

As r₁ < r₂

∴ F₁ > F₂

∴ F_net = F₁ – F₂

4. (d) Trypsin digests proteins and lipase digests emulsified fats.

Explanation :

Pancreatic juice contains the digestive enzymes amylases, lipases, and trypsin, which are secreted by the pancreas. Amylase degrades starch, trypsin degrades proteins, and lipase degrades emulsified lipids.

5. (d) Aqua regia

Explanation :

Aqua regia is a mixture of hydrochloric acid and nitric acid in a ratio 3 : 1 and it can dissolve noble metals such as gold, palladium, and platinum, which, however are not soluble in either of the acids alone.

6. (d) 25 W

Explanation :

We know that,

$$\text{P}=\frac{\text{V}^{2}}{\text{R}}$$

Where, P = Electric power

V = Potential difference in a circuit

R = Resistance

$$\text{Now,\space}\text{R}=\frac{\text{V}^{2}}{\text{P}}\\\text{R} =\frac{220 × 220}{100}=484Ω$$

As the voltage drop across the bulb is 110 V. The power consumed by the bulb is:

$$\text{P}_{b}=\frac{\text{V}^{2}}{\text{R}}\\=\frac{110×110}{484}$$

P_b = 25 W

Hence, the power consumed will be 25 W.

7. (a) (i) and (ii)

Explanation :

Offspring have greater similarity as only one parent is involved in asexual reproduction thus no gametes are formed. The basis of asexual reproduction is mitosis (division of a nucleus into two identical daughter nuclei). Each daughter nucleus has same genetic make up because of replication of parental DNA. The new offspring produced are called clones.

8. (a) A: Initial injury, B: Blastema formation and cell division, C: New tissue formation and functional recovery.

Explanation :

The correct sequence of stages shown in the diagram is:

(a) Initial injury: This is the stage where the flatworm is damaged or injured, leading to tissue loss or disruption.

(b) Blastema formation and cell division: After the initial injury, specialized cells called blastemal cells gather at the injury site. These cells undergo rapid division, forming a mass of undifferentiated cells known as blastema. The blastema serves as the source for regenerating new tissues.

(c) New tissue formation and functional recovery: The blastemal cells differentiate and undergo further cell division to regenerate specific tissues, such as muscle, nerves, and digestive structures. Over time, these newly formed tissues develop and integrate into the existing structures, resulting in functional recovery of the damaged area.

9. (a) White

Explanation :

When the magnesium ribbon is burned in the air, it burns with the white dazzling flame leading to the formation of the white colour ash, which is magnesium oxide.

10. (c) 50 Ω

Explanation :

We know that

Total Resistance

R = R₁ + R₂

= 10 + 40

= 50 Ω

Hence, the value of X is 50 Ω.

11. (b) Yeast, mushroom, bread mould

Explanation :

Yeast, mushrooms, and bread mould all exhibit a saprophytic mode of nutrition. They use digestive enzymes secreted outside their body to break down complex organic substances and absorb basic molecules as nutrition.

12. (a) breaking up of filaments into smaller bits.

Explanation :

In Spirogyra, asexual reproduction takes place by fragmentation, i.e., the organism simply breaks up into smaller pieces upon maturation. Each piece grows into a new individual without forming any gametes.

13. (c) 2 A

Explanation :

A cylindrical conductor of length ‘l’ and uniform area of cross-section ‘A’ has resistance ‘R’. The area of cross-section of another conductor of same material and same resistance but of length ‘2l’ will be 2 A. This can be explained as :

$$\text{R}=\rho\frac{l}{\text{A}}\\\frac{\text{R}_{1}}{\text{R}_{2}}=\bigg(\frac{\text{L}_{1}}{\text{L}_{2}}\bigg)×\bigg(\frac{\text{A}_{2}}{\text{A}_{1}}\bigg)\\\text{A}_{2}=\bigg(\frac{\text{R}_{1}}{\text{R}_{2}}\bigg)×\bigg(\frac{\text{L}_{2}}{\text{L}_{1}}\bigg)×\text{A}_{1}\\\text{A}_{2}=\bigg(\frac{\text{R}}{\text{R}}\bigg)×\bigg(\frac{2l}{l}\bigg)×\text{A}_{1}$$

A₂ = 2 A₁

14. (a) Homozygous

Explanation :

Mendel’s law of dominance states that in a heterozygote, one trait will conceal the presence of another trait for the same characteristic. Rather than both alleles contributing to a phenotype, the dominant allele will be expressed exclusively. The recessive allele will remain “latent,” but will be transmitted to offspring by the same manner in which the dominant allele is transmitted. The recessive trait will only be expressed by offspring that have two copies of this allele.

15. (d)

Explanation :

As when current flows through and current-carrying wire, then direction of magnetic field is calculated by right hand thumb rule.

16. (a) 2 : 1

Explanation :

The number of chromosomes in human sperm is half the number of chromosomes in a zygote i.e., their ratio is 2 : 1.

17. (a) Both A and R are true and R is the correct explanation of A.

Explanation :

A force is always exerted due to magnetic field in the same way electric current flowing through any conductor produces magnetic field. And in this case, Fleming’s left-hand rule is used to predict the directions of the magnetic field, current and displacement.

18. (c) A is true but R is false.

Explanation :

The flowers of pea plants are bisexual and they are self-pollinating, thus, self and cross pollination can easily be performed. They have a shorter life span and are the plants that are easier to maintain. Thus, Mendel choose the pea plant.

19. (b) Both A and R are true and R is not the correct explanation of A.

Explanation :

The person cannot see the objects distinctly and comfortably because of accommodation. The vision becomes blurred due to the refractive defects of the eye.

20. (b) Both A and R are true and R is not the correct explanation of A.

Explanation :

The presence of an X chromosome is essential for the development of female characteristics, it is the presence or absence of the Y chromosome that primarily determines the development of male characteristics.

In humans, individuals with two X chromosomes (XX) typically develop as females, while individuals with one X and one Y chromosome (XY) typically develop as males.

The reason provided is not a complete and accurate explanation of why XX chromosomes give rise to female children and XY chromosomes give rise to male children. The sex determination in humans is a more intricate process involving the presence or absence of specific genes on the sex chromosomes.

Section-B

21. We know that,

$$\text{Refractive index =}\\\frac{\text{Speed of light in air}}{\text{Speed of light in medium}}$$

So, the speed of light in medium =

$$\frac{\text{Speed of light in air}}{\text{Refractive index}}$$

It is obvious from the above relation that the speed of light will be the maximum in that medium which has the lowest refractive index. Now, out of kerosene, turpentine and water, water has the lowest refractive index of 1.33. So, the light will have a maximum speed in the water.

The ray of light passing through the centre of curvature of a concave mirror gets reflected among the same path after a reflection because the angle of incidence is 0°. That is the ray passing through the centre of curvature is incident normally to the mirror. The angle of reflection should also be 0°.

22.

Acids	Bases
Acids are sour in taste.	Bases are bitter in taste.
Acids turn blue litmus to red.	Bases turns red litmus to blue.
An acid is a substance which gives H⁺ ions in a water solution.	A base is a substance which gives OH^– ions in a water solution.
The orange colour of Methyl orange Indicator changes to red in acidic medium.	The orange colour of the Methyl Orange Indicator changes to yellow in bases.
pH value of the acid is less than 7.	pH value of the base is greater than 7.
When non-metallic oxides are dissolved in water, they form acids. $$\text{SO}_{3} + \text{H}_{2}\text{O}\xrightarrow{}\text{H}_{2}\text{SO}_{4}$$	When metallic oxides are dissolved in water they form bases. $$\text{CaO} + \text{H}_{2}\text{O}\xrightarrow{}\text{Co(OH)}_{2}$$

23. (i) Photo-dissociation of ozone and generation of ozone are the two reactions which are in equilibrium thereby maintaining a steady concentration of ozone in the ozonosphere.

(ii) Ultraviolet radiations from the sun are being absorbed by the ozone for the occurrence of given two reactions.

24. After fertilization, the zygote divides several times to form an embryo. The fertilized ovule forms a seed. The seed contains an embryo, enclosed in a protective covering, called the seed coat. As the seed grows further, other floral parts wither and fall off. This leads to the growth of the ovary, which enlarges and ripens to become a fruit with a thick wall called the pericarp.

(i) The transport of food from leaves to other parts of the plant is called translocation. Translocation is essential for plants because without it food prepared by the leaves cannot reach other parts of the plant for their growth and development.

(ii) The substances in plants reach other tissues in plants from the leaves because of translocation.

25. Different functions performed by the pancreas in our body are:

Pancreas makes two hormones i.e., insulin and glycogen that regulates blood sugar level.
It secretes pancreatic juice that aids in the digestion of food.

26.

Section-C

27. When Mendel crossed pure pea plants with round, yellow seeds with pure plants with wrinkled, green seeds in F₁ generation all pea plants with round and yellow seeds were produced. This shows that round and yellow are dominant characters whereas green and wrinkled are recessive characters. Again, when these F₁ plants were crossed round, yellow pea plants, as well as green, wrinkled seeds pea plants were produced. But in addition to these two new characters were produced i.e., round and green, wrinkled and yellow seeds pea plants were produced.

This shows that two pair of characters combines in the F₁ generation, but they get separated and behave independently in F₂generation.

Gametes→ ↓	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy	RrYy	Rryy
rY	RrYy	RrYy	rrYY	rrYy
ry	RrYy	Rryy	rrYy	rryy

Round-yellow, round-green, wrinkled-yellow, wrinkled-green – 9:3:3:1

28. Given: R₁ = 2 Ω, R₂ = 3 Ω, R₃ = 4 Ω

(i) In series, the equivalent resistance is

R_s = R₁ + R₂ + R₃

= 2 + 3 + 4

= 9 Ω

(ii) In parallel, if the equivalent resistance is R_p, then

$$\frac{1}{\text{R}_{\text{p}}}=\frac{1}{\text{R}_{1}} +\frac{1}{\text{R}_{2}} +\frac{1}{\text{R}_{3}}\\\text{or}\space\frac{1}{\text{R}_{\text{p}}}=\frac{1}{2} + \frac{1}{3} +\frac{1}{4}=\frac{13}{12}\\\text{or}\space\text{R}_{p}=\frac{12}{13}=0.92\space Ω$$

29. (i) The reactivity of metals is important in jewelry making. It should be non-reactive to avoid tarnish on the metal. Because electronegativity and nonmetallic character grow from left to right in the periodic table, the oxidizing power of elements increases. Gold, silver and platinum are hence poor oxidizing agents.

They are very lustrous, corrosion-resistant metals. They have strong durability. They may be molded in to any shape or pattern due to their extreme malleability and ductility.

Therefore, Platinum, Gold, and Silver are used to make jewelry.

(ii) Sodium, potassium, and lithium are stored in kerosene because they are very reactive metals and react very vigorously with air as well as water. They are kept immersed in kerosene oil in order to prevent their contact with air and moisture.

(iii) Aluminium is a highly reactive metal, but it is resistant to corrosion. The reason for this is that aluminium reacts with oxygen present in the air to form a thin layer of aluminium oxide. This oxide layer is very stable and prevents further reaction of aluminium with oxygen. It is light in weight and a good conductor of heat. Therefore, it is used to make utensils for cooking.

30. The characteristics of energy transfer in biosphere are:

The ultimate source of energy is the Sun and is converted from one form to another.
Energy is continuously transferred the through food chain and energy flow is unidirectional.
There is a loss of some energy during transfer from one trophic level to the next.
Only 10% of energy is transferred from one trophic level to the next. The solar energy trapped by producers does not revert back to the sun.
At each trophic level, some of the energy is utilised by organisms, the rest is lost to the environment and only 10% is available to the next trophic level.

31. (i) Metals low in reactivity series are obtained by the method of heating their oxides with carbon.

(ii) Y is in the middle of the series, it can be obtained by heating with a reducing agent like carbon or highly reactive metals like Na, Ca and Al.

(iv) Metal Z is high up in the reactivity series. It can be obtained by electrolytic reduction.

(i) Zinc and Iron.

(ii) Dilute hydrochloric acid and dilute sulphuric acid.

(iii) Hydrogen

(iv) Lighter than air

(v) Exothermic

32. (i) Right-hand thumb rule which states that if we hold the current carrying conductor in our right hand such that the thumb points in the direction of flow of current, then the fingers encircle the wire in the direction of the magnetic field.

(ii) The direction of force on a current-carrying conductor placed in a magnetic field is obtained by the Fleming’s left hand rule.
This rule states that “ When forefinger, central finger and thumb of the left hand are stretched in such a way that they are mutually perpendicular to each other, if the forefinger indicates the direction of magnetic field, central finger indicates the direction of the current, then the thumb will indicate the direction of motion of the conductor i.e., the force on the conductor.

(iii) No force acts on a current carrying conductor when the current in conductor is parallel to the magnetic field.

The maximum force is exerted on the current carrying conductor if it is perpendicular to the direction of the magnetic field.

33. (i) (a) It is alkaline in nature as it neutralises the excess acid produced in our stomach and gives us relief from acidity. So, it is used as an antacid.

(b) Baking soda releases carbon dioxide gas which makes the cake or bread soft and spongy. So, it is used in the baking industry.

(c) Baking soda and sulphuric acid present in soda–acid fire extinguisher reacts to release carbon dioxide gas and this gas is a non–supporter of combustion thus, cutting air supply and the fire gets extinguished.

(ii) Acids like HCl and sulphuric acid react with metals to liberate hydrogen gas.

$$\text{Zn + 2HCl}\xrightarrow{}\text{ZnCl}_{2} + \text{H}_{2}\\\text{Mg + H}_2\text{SO}_4\xrightarrow{}\text{MgSO}_{4} +\text{H}_{2}$$

But nitric acid does not react with metals to liberate hydrogen gas as it is a strong oxidising agent.

But magnesium and manganese metal when react with very dilute nitric acid they liberate
hydrogen gas.

$$\text{Zn + 4HNO}_{3}\xrightarrow{}\\\text{Zn(NO}_{3})_{2} +2\text{H}_{2}\text{O} + \text{NO}_{2}\\\text{Mg + 2HNO}_{3}\xrightarrow{}\text{Mg(NO}_3)_2 + \text{H}_2\\\text{Mn + 2HNO}_{3}\xrightarrow{}\text{Mn(NO}_{3})_{2} + \text{H}_{2}$$

Section-D

34. (i) (a) Each piece regenerates into a new Planaria.

(b) When a mature Spirogyra filament attains considerable length it breaks into two or more
fragments and each fragment grows into a new individual.

(c) On maturation when sporangia bursts, spores are liberated, and they are dispersed. On getting a suitable substratum and under favourable conditions each spore germinates into new mycelium.

(ii) (a) Fine adjustment screws were moved to focus the slides.

(b)

(iii) The advantages of sexual reproduction over asexual reproduction are :

Variations are produced due to sexual reproduction which helps in better survival of off springs in the changing environment.
More diversity is seen in the case of sexual reproduction as compared to asexual reproduction.
Due to recombination and crossing over in the meiosis process during the formation of gametes and as there is a mixing of male and female gametes, genetic variations are seen, which is the
main cause of evolution.

Placenta: It is the physical barrier connecting the embryo in the mother’s womb to the uterine wall to allow nutrient uptake, waste removal etc.

Structure: Human placenta is 22 cm in length 2–2.5 cm in thickness, and weight 500 g. It has a dark reddish-blue or crimson colour. It is discoidal in shape.

Functions: This provides a large surface area for glucose and oxygen to pass from the mother to the embryo, and the developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta. Thus, it provides nourishment to the embryo, helps in excretion and provides immunity to the foetus.

35. (i) (a) Two observations are:

Green colour ferrous sulphate crystals will first turn into a dirty white solid and then into a brown residue.
A gas is evolved with a pungent, suffocating smell.

$$\text{(c)}\space\text{2 FeSO}_{4}\xrightarrow{\Delta}\text{Fe}_{2}\text{O}_{3} +\text{SO}_{2} +\text{SO}_{3}.$$

(ii) (a) When an aqueous solution of sodium sulphate reacts with an aqueous solution of barium chloride, the product formed is barium sulphate i.e., a white precipitate. The reaction will not take place if the reactants are in a solid state. It is a double displacement type of reaction.

$$\text{BaCl}_{2}(aq) + \text{Na}_{2}\text{SO}_{4}\text{(aq)}\xrightarrow{}\\\text{BaSO}_{4}(s) + 2\text{NaCl}(aq)$$

(b) When iron nails are placed in copper sulphate solution for half an hour, iron sulphate solution and copper metal is formed.

$$\text{CuSO}_{4}(aq) + \text{Fe(s)}\xrightarrow{}\\\text{FeSO}_{4}(aq) + \text{Cu(s)}$$

This reaction occurs because iron is more reactive than copper. Also, a brown substance will be deposited on the iron nails. The deposited substance is nothing but copper.

(a) 7

(b) Base

(d) The concentration of hydronium ion decreases.

(e) Alkalis

36. (i) No, the eye lens is not made of glass, it is made of fibrous jelly like material.

(ii) We know,

P = – 0.2 D

$$f =\frac{1}{\text{P}}=\frac{1}{\text{-0.2}} =-5m$$

Distance of far point of his eye is 5 m.

(iii) (b) Concave lens

(iv) (d) Retina

(i) The image of any object formed on the retina persists for about 1/16 of a second. This continuance of sensation of eye for sometime even after the removal of the object is called persistence of vision.

(ii) The angle between the incident ray produced forward and the emergent ray produced backward is called angle of deviation.

(iii) The ability of the eye lens to adjust its focal length, is called the power of accommodation. There should be a contraction of ciliary muscles, that will increase the curvature of the eye lens and becomes thicker, so the focal length of the eye lens will decrease. It will thus enable us to see the objects clearly.

Section-E

37. (a) Father determines the sex of a child. It is therefore thought that genes for femaleness is associated with the X chromosomes and genes for maleness are on Y chromosomes. Hence, the presence of the Y chromosome is a must for the determination of sex of the male person. When fertilisation takes place between a sperm carrying the X chromosome and an egg cell with the X chromosome; then, the developed zygote will contain an XX combination, the child will be a girl. If a sperm carrying Y chromosome unites with an egg cell containing the X chromosome then the zygote will carry XY chromosome and the child will be a boy.

Hence, it can be concluded that the sex of the baby is depended on the father.

(b) The child will be boy (Male)

23 pairs out of which twenty-two of these pairs, are called autosomes, they look the same in both males and females. One pair called sex chromosomes are different in both male and female.

38. (a) The above activity shows Displacement reaction.

(b) The reason for this can be understood with the help of the following reaction,

$$\underset{\text{(Copper sulphate)}}{\text{Fe(s)} + \text{CuSO}_{4}(aq)}\xrightarrow{}\\\underset{\text{(Iron sulphate)}}{\text{FeSO}_{4}(aq)} + \text{Cu(s)}$$

In this reaction, iron has displaced or removed another element, copper, from the copper sulphate solution. Therefore, the iron nail becomes brownish in colour and the blue colour of copper sulphate solution fades.

Hence, the given reaction is not possible.

$$\underset{\text{(Copper sulphate)}}{\text{Zn(s)} + \text{CuSO}_{4}(aq)}\xrightarrow{}\\\underset{\text{(zinc sulphate)}}{\text{ZnSO}_{4}(aq)} + \text{cu(s)}\\\text{Pb(s)} + \underset{\text{Copper chloride}}{\text{CuCl}_{2}(aq)}\xrightarrow{}\\\underset{\text{(Lead chloride)}}{\text{PbCl}_{2}(aq)} + \text{Cu(s)}$$

39. (i) 220 V

(ii) Two separate circuits are used, one of 15 A current ratings for appliances with higher power ratings such as geysers, air coolers, etc. The other circuit is of 5 A current rating for bulbs, fans, etc.

(iii) The earth wire, which has insulation of green colour, is usually connected to a metal plate deep in the earth near the house.

(iv) It is used as a safety measure, especially for appliances with a metallic body, for example, electric press, toaster, table fan, refrigerator, etc. The metallic body is connected to the earth wire, which provides a low-resistance conducting path for the current. Thus, it ensures that any leakage of current to the metallic body of the appliance keeps its potential to that of the earth, and the user may not get a severe electric shock.