Solved 2023 Question Paper CBSE Class 10 Science

it turns milky due to formation of calcium carbonate and on passing excess of carbon dioxide it becomes colourless due to formation of calcium hydrogen carbonate which is soluble in water.

Reason — The reaction between sodium carbonate and HCl gas produces carbon dioxide gas.

Na₂CO₃ + 2HCl (dil.) ⟶ 2NaCl + H₂O + CO₂

Solution X is aq. calcium hydroxide which reacts with carbon dioxide gas and forms calcium carbonate, which turns the solution milky.

Ca(OH)₂ + CO₂ ⟶ CaCO₃ + H₂O

However, on passing excess carbon dioxide, the calcium hydrogen carbonate is formed, which is soluble in water and hence, the solution X becomes colourless.

CaCO₃ + H₂O + CO₂ ⟶ Ca(HCO₃)₂

thermal decomposition of lead nitrate which produces brown fumes of nitrogen dioxide.

Reason — Thermal decomposition of lead nitrate takes place which produces brown fumes of nitrogen dioxide.

2Pb(NO₃)₂ ⟶ 2PbO + 4NO₂ + O₂

4, 2, 1

Reason — The balanced equation is as follows:

MnO₂ + 4HCl ⟶ MnCl₂ + 2H₂O + Cl₂

Reason — For lemon juice pH is 3 but colour of pH paper is orange and nature is given as basic which is incorrect. For Gastric juice, pH value of 6 is incorrect. For pure water, colour of pH paper is incorrect. It should be green not yellow.

Al and Al₂O₃

Reason — Aluminium is used in thermite process. When aluminium is heated in oxygen it forms aluminium oxide which is amphoteric in nature .

4Al + 3O₂ ⟶ 2Al₂O₃

Na₂CO₃.10H₂O

Reason — The formula of washing soda is : Na₂CO₃.10H₂O

A is a saturated cyclic hydrocarbon and B and C are unsaturated cyclic hydrocarbons.

Reason — A is having all the single bonds hence it is a saturated hydrocarbon whereas B and C have double bonds so they are unsaturated cyclic hydrocarbons.

a fungi, Rhizopus

Reason — Fungi show extra-cellular digestion. The cell wall of fungi secretes enzymes that digest the food outside the body of fungi. The digested food is then absorbed by the fungi.

The villi of the small intestine absorb water from the unabsorbed food before it gets removed from the body via the anus.

Reason — The villi of the small intestine absorbs digested food. Excess water is absorbed in large intestine.

In individuals of a given species, a specific gene is located on a particular chromosome.

Reason— In individuals of a given species, each gene has a fixed locus on a specific chromosome.

It is a growth related movement.

Reason — Tropic movement in plants is related to growth. It occurs in stem as well as roots. It is affected by touch, gravitation and light.

Rose, root

Reason— Rose is propagated by stem.

16

Reason — Four identical resistors of resistance 8 Ω are connected in series :

So, R_s = 8+8+8+8 = 32 Ω

When connected in parallel:

$\dfrac{1}{R_p}$ = $\dfrac{1}{8}$ + $\dfrac{1}{8}$ + $\dfrac{1}{8}$ + $\dfrac{1}{8}$

$\dfrac{1}{R_p}$ = $\dfrac{1+1+1+1}{8}$ = $\dfrac{4}{8}$ = $\dfrac{1}{2}$

So, R_p = 2 Ω

$\dfrac{R_s}{R_p}$ = $\dfrac{32}{2}$ = 16

higher power ratings such as geyser.

Reason — As P = i²R

Hence, in domestic electric circuits the wiring with 15 A current rating is for the electric devices which have higher power ratings such as geyser.

0.15 V and 1.8 V

Reason — Least count of any scale is the value measured by a single division on it.

10 div = 1.5 V

So, 1 div = $\dfrac{1.5}{10}$ = 0.15 V

Hence, least count = 0.15 V

Reading shown = least count x no. of div. = 0.15 x 12 = 1.8 V

Hence, Reading shown = 1.8 V

zero

Reason — The magnetic fields produced at the midpoint P, by the currents flowing in the same direction in the two parallel wires will be equal in magnitude but opposite in direction.

Hence, the resultant magnetic field at P will be zero.

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

Reason — When a piece of lead is added to an aqueous solution of copper sulphate, a displacement reaction takes place as lead is more reactive than copper hence lead displaces copper from the copper sulphate solution. The chemical equation for the reaction is:

Pb + CuSO₄ ⟶ PbSO₄ + Cu

This results in a colorless solution [PbSO₄].

(A) is true, but (R) 1s false.

Reason — Sex of a child is decided by the chromosome (X or Y) of father that is inherited by the embryo. Genes on chromosome Y are responsible for male child.

(A) is true, but (R) is false.

Reason — Blood clotting is due to blood platelets, fibrinogen and Prothrombin.

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

Reason — Magnetic field strength is directly proportional to the number of turns of the circular coil. Hence, strength of the magnetic field increases on increasing the number of turns in it because current in each circular turn has the same direction and the magnetic field due to each turn then just adds up.

(i) Plaster of paris — CaSO₄.$\dfrac{1}{2}$H₂O

(ii) Difference in chemical composition between baking soda and baking powder:

(i) When blue coloured copper sulphate crystals are heated :

CuSO₄.5H₂O $\xrightarrow{\Delta}$ CuSO₄ + 5H₂O

(ii) When sodium hydrogen carbonate is heated during cooking

2NaHCO₃ $\xrightarrow{\Delta}$ Na₂CO₃ (s) + H₂O (l) + CO₂ (↑)

(a) The role of insulin in regulating blood sugar levels in human body are:

1. It promotes glucose utilisation by the body cells, thereby reducing the blood sugar level.
2. It stimulates deposition of extra glucose of the blood as glycogen in liver and muscles.

(b) The timing and amount of release of insulin is regulated by the feedback mechanism. Insulin is released by beta-cells of pancreas when there is increase of sugar level in blood. The amount of insulin is also decided by the amount of sugar in the blood. When the level of sugar in the blood decreases the negative feedback will allow the pancreas to stop the secretion of insulin.

(i) Vena cava: It transports deoxygenated blood from whole body to the heart.

(ii) Pulmonary artery: It transports deoxygenated blood from the heart to lungs.

Below schematic flow chart shows the breakdown of glucose in a cell in the presence and absence of oxygen:

The part of the human excretory system where nephrons are found are Kidneys.

Structure of Nephron — Nephron is the basic filtration unit in the kidney. It consists of a tubule which is connected with a collecting duct at one end and a cup shaped structure at the other end, called Bowman's capsule. Every Bowman's capsule contains a cluster of capillaries called glomerulus within the cup-shaped structure.

Function of Nephron — The blood enters into glomerulus through afferent arteriole of renal artery and leaves it through efferent arteriole. This causes filtration of the blood. Then the filtrate passes into the tubular part of the nephron. Here, useful substances such as glucose, amino acids, salts and some water are re-absorbed into the blood by the capillaries surrounding the nephron tubule. The filtrate which remains after the re-absorption is called the urine, which is collected from nephron by the collecting duct to carry it to the urinary bladder and then to the urethra.

The path of the emergent beam is shown in the diagram below:

The phenomenon of the splitting up of the white light into its constituent colours is called dispersion of light.

The cause of dispersion of white light is the change in speed of light with wavelength.

When white light enters the first surface of a prism, light of different colours due to their different speeds in glass, get deviated through different angles towards the base of the prism. On the second surface of prism, only refraction takes place (from glass to air) and different colours are deviated through different angles. As a result, colours get further separated on refraction at the second surface.

(i) The power of an eye to see nearby objects as well as far off objects diminishes with age because the power of accommodation of the eye usually decreases with ageing due to weakening of ciliary muscles and decrease in flexibility of eye lens.

(ii) The defect that is likely to arise in the eyes in such a condition is Presbyopia. For most people, the near point gradually recedes away. They find it difficult to see nearby objects comfortably and distinctly without corrective eye-glasses.

(iii) Presbyopia can be corrected by using a convex lens as shown in the diagram below:

Several pesticides and other chemicals are used to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain. As these chemicals are not degradable, these get accumulated progressively at each trophic level.

(a) The reducing agents are:

(i) Ammonia (NH₃)

(ii) Water (H₂O)

(iii) Carbon monoxide (CO)

(iv) Hydrogen (H₂)

(b) A redox reaction is one in which one reactant gains oxygen and becomes oxidized while the other reactant loses oxygen and is reduced.

For example :

CuO + H₂ ⟶ Cu + H₂O

Hydrogen is oxidized to water and CuO is reduced to Cu

(a) (i) Production of too much acid in stomach during indigestion leads to pain and irritation. Antacid is given in such case to neutralize the acid of the stomach. The antacids neutralise the excess acid. Magnesium hydroxide (milk of magnesia) is a mild base, often used for this purpose.

(ii) In case of a honeybee sting formic acid is released into the skin which causes pain and irritation. To reduce the pain caused due to the sting, bases like baking soda are used which neutralize acid and relieve the pain. Stinging hair of nettle leaves inject methanoic acid causing burning pain. It is also treated with rubbing mild base.

(b) When the milk is turned into curd then its pH value decreases. This is due to the production of lactic acid in curd which is acidic in nature.

(i) ATP is consumed in glycolysis to convert glucose to pyruvate. It is also produced in electron transport chain.

(ii) Maximum amount of gaseous exchange occur in plants through stomata and lenticels present on leaf and stem surface respectively and the large inter-cellular spaces ensure that all cells are in contact with air.

(iii) The direction of diffusion depends upon the environmental conditions and the requirements of the plant. At night, when there is no photosynthesis occurring, CO₂ elimination is the major exchange activity going on. During the day, CO₂ generated during respiration is used up for photosynthesis, hence there is no CO₂ release. Instead, oxygen release is the major event at this time.

(i) Internal Energy reserve in plants is starch and in animals it is glycogen.

(ii) Desert plants take up carbon dioxide at night and prepare an intermediate which is acted upon by the energy absorbed by the chlorophyll during the day.

(a) The completed ray diagram showing the formation of image is given below:

(b) The image formed is virtual, erect, diminished and located behind the mirror between P and F.

(c) positive

(a) Red colour has the longest wavelength and it deviates the least, hence, danger signals installed at airports and at the top of tall buildings are of red colour so that they can be easily seen from a distance.

(b) Scattering of light takes place because of the particles present in the atmosphere. At high altitude, the atmospheric medium is rarer so the scattering of light taking place is very low. Hence, the sky appears dark to passengers flying at high altitudes.

(c) The path of a beam of light passing through a colloidal solution is visible due to scattering of light by colloidal particles and this is known as Tyndall effect.

(i) Fleming's left hand rule is used to find the direction of force acting on a current carrying conductor, placed in a magnetic field.

According to this rule : Stretch the thumb, fore finger and middle finger of your left hand such that they are mutually perpendicular. If the forefinger points in the direction of magnetic field and the middle finger in the direction of current, then the thumb will point in the direction of motion or force acting on conductor.

(ii) (1) Force on electron is maximum in case (i) because here direction of motion of electron is at right angles to the magnetic field.

(2) Force on electron is minimum in case (iii) because here direction of motion of electron is along the direction of the magnetic field.

(i)

(1) The pattern of magnetic field lines of a current carrying solenoid is shown below:

(2) The pattern of magnetic field lines of a bar magnet is shown below:

(ii) Distinguishing features between :

(i) Kitchen garden is known as artificial ecosystem because the biotic and abiotic factors are modified by humans and not decided by the nature as in natural ecosystems like forest. In forests, humans do not modify biotic or abiotic factors.

(ii) Two things to be kept in mind to convert an artificial ecosystem into a self-sustaining system are:

1. Balance between producers and consumers — We should select inter-dependable producers and consumer to make the ecosystem self sustainable. They should form food web so that their population is controlled.
2. Waste management — The involvement of decomposers is very important for sustainable ecosystem.

Natural ecosystems are self sustaining due to a perfect relation of interdependence. For converting an artificial ecosystem into a self-sustaining system we should try to minimize human interference and include organisms that make it sustainable.

(i) Plants → Rat → Snake → Hawk

(ii) According to the 10% rule of energy transfer, 10% of energy is transferred to next trophic level. Amount of energy available to second trophic level = 20,000 J Therefore, amount of energy transferred to third trophic level = 10% of 20,000 J = 2000 J. And, amount of energy transferred to fourth trophic level = 10% of 2000 J = 200 J

(i) Compounds A, B and C are:

A → Ethanol
B → Ethene
C → Ethane

C₂H₅OH${\xrightarrow{\text{Conc. sulphuric acid}}}$ CH₂=CH₂

CH₂=CH₂ + H₂ ${\xrightarrow{\text{Ni}}}$ CH₃-CH₃

(ii) C₂H₅OH${\xrightarrow{\text{Conc. sulphuric acid}}}$ CH₂=CH₂

(iii) When ethane undergoes combustion, carbon dioxide is produced along with water and heat.

2C₂H₆ + 7O₂ ⟶ 4CO₂ + 6H₂O + Heat

(iv) In industry, hydrogenation reaction is used for preparing vegetable ghee from vegetable oils

(v) Sodium ethoxide and Hydrogen
2Na + 2C₂H₅OH ⟶ 2C₂H₅ONa + H₂

(i) Diagram showing the formation of micelles when soap is applied on oily dirt is given below:

(ii) The test tube containing detergents (i.e. Y) will form more foam because detergents are generally ammonium or sulphonate salts of long carboxylic acids. The charged ends of these compounds do not form insoluble precipitates with the calcium and magnesium ions in hard water. Hence, detergents remain effective even in hard water.

(iii) The test tube containing soap (i.e. X) will show a curdy white precipitate because soap molecules react with calcium and magnesium salts of hard water and form the floating off-white layer over water called as scum.

(a) Calyx and corolla are the parts of a bisexual flower that are not directly involved in reproduction. Calyx has a protective function while corolla attracts pollinators.

(b)

Significance of pollination — Two significance of pollination are:

1. It helps in the production of fruits and seeds.
2. It helps in the transfer of characters and traits from both the parents to the offspring.

(c) Ovules mature to form seed and ovary grows to form fruit.

(a) Given,

Power (P) = 880 W [when heating is at the maximum rate ]

Power (P) = 330 W [when heating is at the minimum rate ]

Voltage (V) = 220 V

Case I : When heating is at the maximum rate

We know,

P = VI

Substituting we get,

880 = 220 x I

I = $\dfrac{880}{220}$ = 4 A

From V = IR

Substituting we get,

220 = 4 x R

R = $\dfrac{220}{4}$ = 55 Ω

Hence, when heating is at the maximum rate, I = 4 A and R = 55 Ω

Case II : When heating is at the minimum rate

Substituting we get current (I)

330 = 220 x I

I = $\dfrac{330}{220}$ = $\dfrac{3}{2}$ = 1.5 A

Substituting we get resistance (R),

220 = 1.5 x R

R = $\dfrac{220}{1.5}$ = 1.46 Ω

Hence, when heating is at the minimum rate, I = 1.5 A and R = 1.46 Ω

(b) When the electric circuit is purely resistive, that is, a configuration of resistors only connected to a battery; the source energy continually gets dissipated entirely in the form of heat. This is called heating effect of electric current.

(c) H = I²Rt where

This is known as Joule's law of heating.

(a) When copper is heated in air, it reacts with the oxygen present in air to form black copper oxide.

2Cu(s) + O₂(g) $\xrightarrow{\Delta}$ 2CuO(s)

(b) Amphoteric metal oxides behave both as acidic as well as basic oxides.

Example : Aluminium oxide [Al₂O₃]

It reacts with hydrochloric acid to form water and aluminium chloride

Al₂O₃ + 6HCl ⟶ 2AlCl₃ + 3H₂O

It reacts with sodium hydroxide solution and produces water and sodium aluminate (NaAlO₂).

Al₂O₃ + 2NaOH ⟶ 2NaAlO₂ + H₂O

(c)

(i) Na₂O(s) + H₂O(l) ⟶ 2NaOH

(ii) Al₂O₃ + 2NaOH ⟶ 2NaAlO₂ + H₂O

OR

(i) S + O₂ ⟶ SO₂

(ii) Sulphur dioxide gas is produced.

(iii) Sulphur dioxide is a non-metal oxide and acidic in nature.

(iv) As the litmus paper is dry there will be no change in colour of litmus.

(a) Two pairs of other contrasting characteristics of pea plant used by Mendel are:

1. Purple flower and white flower
2. Tall plant and short plant

(b) Differences between dominant and recessive traits:

(c) All plants in F₁ generation (in the above case) will have round and yellow seeds. In F₂ generation, the phenotypic ratio will be 9:3:3:1.

It is clear from the result that the allele showed independent assortment during gamete formation and combined to give four different phenotypes in ratio 9:3:3:1.

OR

(c) Diagram explaining the type of progeny in F₁ generation and F₂ generation is shown below:

Violet flower colour is dominant trait and white flower colour is recessive trait in pea. When pure violet flowered plant (VV) is crossed with pure white flowered plant (vv), the F₁ generation will have all violet flowered plants (Vv). In F₂ generation, the ratio of plants with purple flower and white flower will be 3:1. The genotypic ratio will be 1:2:1.

(a) Two applications of concave mirror are :

1. As a reflector — They are used in torches and vehicle headlights to get a powerful parallel beam of light.
2. As a shaving mirror — When a concave mirror is held near the face (such that the face is between pole and focus of the mirror), it gives an upright and magnified image. Hence even tiny hair can be seen.

(b) As we know, R = 2f where, R is the radius of curvature and f is the focal length.

Given focal length (f) = 15 cm

So, substituting we get,

R = 2 x 15 = 30 cm

(c) Ray diagram showing the type of image formed when an object is placed between pole and focus of a concave mirror is given below:

OR

(c) Given,

Object distance (u) = -100 cm

Image distance (v) = -100 cm

Focal length (f) = ?

[f in case of a concave mirror is negative.]

Using formula,

$\dfrac{1}{\text{f}}$ = $\dfrac{1}{\text{v}}$ + $\dfrac{1}{\text{u}}$

We get,

$\dfrac{1}{\text{f}}$ = $\dfrac{1}{\text{-100}}$ + $\dfrac{1}{\text{-100}}$

$\dfrac{1}{\text{f}}$ = $\dfrac{2}{\text{-100}}$ = $\dfrac{1}{\text{-50}}$

So, f = -50 cm

Hence, focal length = -50 cm.

(ii) Size of object (h_o) = 10 cm

magnification = ?

From formula,

m = - $\dfrac{\text{v}}{\text{u}}$

Substituting we get,

m = - $\dfrac{-100}{-100}$ = -1

Hence, magnification of the object = -1 i.e., inverted image is formed of same size as object.