Madhyamik Class 10 Physical Science Question Paper Solved 2020

d. CO₂

Explanation: Although CO₂ is a greenhouse gas and contributes to global warming, it does not directly participate in the depletion of the ozone layer.

b. 0.5RT

Explanation:

At STP (Standard Temperature and Pressure), the conditions are:

• Temperature (T) = 273 K
• Pressure (P) = 1 atm
• 1 mole of an ideal gas occupies a volume (V) of 22.4 liters.

Calculation of mole: n = 11.2/22.4 = 0.5

From the ideal gas equation:

PV =nRT

or, PV = 0.5 RT

a. 448 L

Explanation:

Since 1 mole of CH₄ requires 2 moles of O₂,

∴ 10 moles of CH₄ will require = 10 × 2 = 20 moles of O₂

Volume of 20 moles of O₂ = 20 × 22.4 = 448 L

b. Diamond

Explanation: Diamond has the highest thermal conductivity of any known material. Its structure allows for extremely efficient heat transfer.

c. r > v

Explanation: When light passes from one medium to another (air to prism in this case), the amount of bending (refraction) depends on the wavelength of the light.

The refractive index (μ) of a medium is higher for shorter wavelengths (violet) and lower for longer wavelengths (red).

Since the refractive index for violet light is higher, it bends more than red light when entering the prism. This means:

• r (angle of refraction for red light) will be greater than v (angle of refraction for violet light) because violet light bends more.

b. 180°

Explanation: At the center of curvature of a concave mirror, light rays hit the mirror perpendicularly and reflect back along the same path. The angle of deviation is the angle between the incident and reflected ray, which in this case is 180°.

d. Both are points

Explanation: Coulomb’s law applies specifically to point charges, which are idealized as having no size. It describes the force between two point charges. While it can be extended to spherical charges (considered as point charges at their centers), it is most accurate when both charges are points.

d. High resistance, low melting point

Explanation:

A fuse wire is designed to protect electrical circuits by melting and breaking the circuit when current exceeds a safe limit. It needs:

• High resistance: To generate enough heat when excess current flows.
• Low melting point: So it can melt quickly to stop the current and protect the circuit.

c. Two protons, two neutrons

Explanation:

An α-particle (alpha particle) is essentially a helium nucleus, which consists of:

• 2 protons
• 2 neutrons

It has no electrons, making it positively charged. Therefore, the correct composition is two protons and two neutrons.

d. Radioactivity

Explanation: Periodic properties are characteristics of elements that show a trend across the periodic table, such as density, melting point, and boiling point. Radioactivity, however, is not a periodic property because it does not follow a consistent trend and varies widely among elements, particularly among heavy elements.

b. Calcium oxide

Explanation: Calcium oxide (CaO) is an ionic compound that exists as a lattice structure rather than as discrete molecules. In contrast, hydrogen chloride (HCl), methane (CH₄), and ammonia (NH₃) are all molecular compounds composed of individual molecules.

d. the concentration of CuSO₄ in solution remains unchanged

Explanation: The correct statement is: the mass of cathode increases and the mass of anode decreases. The concentration of CuSO4 in the solution remains unchanged.

a. Violet

Explanation:

When H₂S gas is passed through an alkaline aqueous solution of sodium nitroprusside, a violet color is produced. This occurs due to the formation of a complex between sulfide ions and the nitroprusside.

b. Fe₂O₃

Explanation:

The formula for red haematite, an ore of iron, is Fe₂O₃, which indicates it contains two iron atoms for every three oxygen atoms.

d. CH₃COOH

Explanation:

When aqueous NaHCO₃ (sodium bicarbonate) reacts with acetic acid (CH₃COOH), it produces carbon dioxide (CO₂) gas. The reaction is:

CH₃​COOH+NaHCO₃ → CH₃COONa+H₂O+CO₂

Methane is the fuel gas harvested from coal beds, often referred to as coal-bed methane (CBM).

OR

For the second question: The gas in air that contributes to global warming is Carbon dioxide (CO₂).

An energy source that can be used for sustainable development is solar energy.

False

Explanation:

Even at a fixed temperature and pressure, gas molecules in a closed vessel do not all move at the same speed.

The V versus T graph according to Charles’ law is a straight line.

False

Explanation:

Among copper, invar, and iron, invar has the lowest linear expansion coefficient, not iron. Invar is a special alloy designed to have very low thermal expansion.

OR

The unit of the volume expansion coefficient is per kelvin (K⁻¹).

The pole of a spherical mirror is the geometric centre of the mirror’s reflecting surface.

One use of X-rays is in medical imaging to diagnose fractures of bones.

A motor is a machine where electrical energy is converted into mechanical energy.

Neutral wire and the earth (or ground) wire.

Nuclear Fission is the kind of nuclear reaction that produces energy in a nuclear reactor.

OR

A natural radioactive element is Uranium-238 (U – 238).

2.11.1. A transuranic element – (b) Neptunium

2.11.2. A noble element – (a) Krypton

2.11.3. Prepared by carbon reduction of the oxide of the metal – (d) Zinc

2.11.4. In the alloy brass, the metal whose percentage amount is higher than that of the other metal – (c) Copper

Chloroform is not soluble in water. Sodium chloride (table salt) is highly soluble in water.

A metal that is extracted by the process of electrolysis is sodium.

OR

The anode in the electroplating of silver on a brass spoon is the silver electrode.

The energy that causes chemical reactions during electrolysis is electrical energy.

When you add red litmus paper to an aqueous solution of ammonia, it turns blue, indicating that the solution is alkaline in nature.

OR

NaOH + H₂S → Na₂S + H₂O

One use of urea is as a fertilizer.

Structural formula of propanone

OR

Wöhler first prepared the organic compound urea from the inorganic compound ammonium cyanate in the laboratory.

An example of a biodegradable natural polymer is starch.

The troposphere is the layer of the atmosphere where the pressure is the highest. This is because the troposphere contains the majority of the atmosphere’s mass, including water vapor, gases, and particulate matter.

Molar Mass of O₂ = 32

Molar Mass of CO₂ = 44

Moles of O₂ = 32\over 32 = 1

Moles of CO₂ = 44\over 44 = 1

Ideal gases Equation: PV = nRT

or, V ∝ nRT\over P

At constant temperature and pressure, the volume is directly proportional to the number of moles of gas:

V_1\over V_2 =n_1\over n_2

or, V_1\over V_2 =1\over 1

Since both gases have the same number of moles under the same conditions of temperature and pressure, the ratio of their volumes is 1:1.

OR

V_1​ = 520 cm³

V₂​ = 700 cm³

T₁​= −13ºC = 273 – 13 = 260 K

Charles’ Law: V_1\over T_1 = V_2\over T_2

T₂ = V_2\over T_2 × 260 = 350 K

or, T₂ = 350 K – 273 = 77°C

The final temperature is 77°C.

Two Features of the Image Formed by a Simple Camera:

1. Inverted: The image produced by a simple camera is inverted (upside down) relative to the object.
2. Real: The image formed is a real image, meaning it can be projected onto a screen.

OR

The image of an extended object placed at infinity will be formed at the focal point of the concave mirror.

Feature of the Image: The image will be point-sized (highly diminished) and inverted.

Similarity:

Both emf and potential difference measure electrical energy per unit charge.

Dissimilarity:

Emf is the voltage generated by a source with no current, while the potential difference is the voltage between two points when current flows.

An example of an ionic compound that does not obey the octet rule is lithium oxide (Li₂O).

Lithium (Li) has 3 electrons and loses 1 electron to form Li⁺, achieving a stable configuration with only 2 electrons, not 8 (octet).

Oxygen (O) gains 2 electrons to form O^2-, which follows the octet rule.

OR

Sodium chloride (NaCl) has a much higher melting point than glucose because NaCl has strong ionic bonds that require more energy to break. Whereas, glucose has weaker covalent bonds and intermolecular forces, leading to a lower melting point.

Ionic Bond Between Na and F:

• Sodium (Na) (atomic number 11) has 1 electron in its outer shell and tends to lose this electron to achieve a stable electron configuration, forming Na⁺.
• Fluorine (F) (atomic number 9) has 7 electrons in its outer shell and needs 1 more electron to complete its octet, forming F^–.

When Na and F react:  Na+F→Na ⁺ +F ^– (Ionic Bond)

Covalent Bond Between H and F:

• Hydrogen (H) (atomic number 1) has 1 electron and can share it to achieve a stable configuration.
• When H and F combine, they share electrons to complete their outer shells:

When H and F react:  H + F → HF (Covalent Bond)

When nitrogen gas is passed over heated calcium carbide (CaC₂) at 1100°C, calcium cyanamide (CaCN₂) and carbon (C) are formed.

Balanced Chemical Equation:

CaC₂ ​+ N₂ {\overset \text {1100\ °C}{\longrightarrow}} CaCN2​ + C

This reaction is used in the production of calcium cyanamide, which is an important fertilizer.

Balanced Chemical Equation for the Thermit Process:

Fe_2​O₃ ​+ 2Al → 2Fe + Al₂​O₃

​In this reaction, ferric oxide (Fe_2​O₃) reacts with aluminium (Al) to produce metallic iron (Fe) and aluminium oxide (Al₂​O₃).

The thermit process is commonly used for welding railway tracks and repairing metal structures due to the high temperature produced during the reaction.

OR

Balanced Chemical Equation:

Fe + CuSO_4​ → FeSO₄ ​+ Cu

Information from the Reaction:

This reaction shows that iron (Fe) is more reactive than copper (Cu) because iron displaces copper from its compound. Hence, Fe is placed above Cu in the activity series of metals.

Members of a Homologous Series (Alcohols):

The alcohols from the given compounds are:

• CH₃OH (Methanol)
• CH₃CH₂OH (Ethanol)
• CH₃CH₂CH₂OH (Propanol)

OR

A functional group is a specific group of atoms within a molecule that is responsible for the characteristic chemical reactions of that molecule. Functional groups determine the properties and reactivity of organic compounds.

Example:

In ethanol (C₂H₅OH), the functional group is the hydroxyl group (-OH).

Avogadro’s Law: Avogadro’s Law states that, at constant temperature and pressure, equal volumes of gases contain an equal number of molecules.

At a certain fixed temperature and pressure the molar volume (V/n) of the real gases are nearly equal and at STP the limit is 22.4 L mol^-1.

Then, V_1\over n_1 = V_2\over n_2

or, V_1\over n_1 = V_2\over n_2 = K, where K is Avogadro constant,

This implies that V ∝ n

As the number of moles increases, the volume increases, supporting Avogadro’s Law.

For A:

Vapour density of A = 32

Molar Mass of A (M_A) = 2 × 32 = 64

For B:

Vapour density of B = 16

Molar Mass of A (M_A) = 2 × 16 = 32

From the balanced equation:

2A + B → C

The molar mass of C (M_C) can be calculated using the molar masses of A and B:

M_C = 2M_A + M_B

= 2 × 64 + 32

= 160

∴ Vapour density of C = 160\over 2 = 80

OR

(i) According to the equation, 2 moles of ZnS produce 2 moles of ZnO.

So, 100 moles of ZnS will produce 100 moles of ZnO.

Molar mass of ZnO = 65.5 + 16 = 81.5 g

∴ Mass of 100 moles of ZnO = 8150 g

(ii) According to the equation, 2 moles of ZnS produce 2 moles of SO₂.

Therefore, 100 moles of ZnS will produce 100 moles of SO₂.

An example of volume expansion of a liquid is water when heated. As the temperature increases, the molecules gain kinetic energy, causing the water to expand and occupy a larger volume.

Coefficient of Area Expansion (β) :

β = ΔA\over A_1 ΔT

Units: K^-1 or  °C^-1

OR

The conduction of heat through a solid depends on:

1. Material: Different materials have varying thermal conductivities.
2. Temperature difference: A greater temperature difference increases the rate of heat conduction.
3. Cross-sectional Area: Larger areas enhance heat transfer, while greater thickness reduces it.

Dispersion of Light is the process by which white light splits into its constituent colours when it passes through a prism.

No, there will not be a dispersion of white light within a glass slab.

Angle of incidence (i) = 30º

Angle of emergence (e) = 45º

A = 60º (equilateral triangle prism)

Deviation (δ) = i + e -A

= 30º + 45º – 60º

= 15º

The angle of deviation is 15º.

OR

Calculate the Velocity of Light in the Medium

Speed of light in vacuum (c) = 3 × 10⁸ m/s

Refractive index (μ) = 1.5

Velocity of Light in the Medium = 3 × 10^8\over 1.5

= 2 × 10⁸ m/s

Calculate the Wavelength in the Medium

λ₀ = wavelength in air (given as 6000 A˚)

λ = λ_o\over 1.5 = 6 × 10^{-7} \over 1.5

λ = 4 × 10^-7 m = 4000 Å

ρ_A ​= 1.6×10^-8 Ω⋅m

ρ_B​ = 3.2×10^-8 Ω⋅m

R =ρL\over A

A_A\over A_B = ρ_A\over ρ_B

Or, A_A\over A_B = 1.6×10^{-8}\over 3.2×10^{-8}  = 1.6\over 3.2

Or, A_A\over A_B = 1\over 2

The ratio of their cross sections should be = 1 : 2

OR

Calculate the Series Combination

R_s = R₁ + R₂

R_s = 10 Ω + 10 Ω = 20 Ω

Calculate the Parallel Combination

{1\over R_{eq}} = {1\over R_s}  + {1\over R_3}

or, {1\over R_{eq}} = {1\over 20}  + {1\over 20}

or, {1\over R_{eq}} = {1 + 1\over 20}

or, {1\over R_{eq}} = {2\over 20}

or, R_eq = 10 Ω

Electrical power is the rate at which electrical energy is consumed or converted into other forms of energy.

The rating of a bulb as 220 V – 100 W means:

• 220 V: It should be connected to a power supply of 220 volts for optimal performance.
• 100 W: It consumes 100 watts of electrical power, which indicates how much energy it uses per unit of time.

Radioactive rays are emitted from the nucleus of an atom.

Penetrating Power and Ionizing Power

• Gamma rays have the highest penetrating power.
• Alpha particles have the highest ionizing power.

Dissimilarity with Group 1 Elements:

• Hydrogen is a non-metal, whereas group 1 elements are metals.

Dissimilarity with Group 17 Elements:

• Valence electron: Hydrogen has 1 valence electron, while group 17 elements have 7 valence electrons.
• Hydrogen follows the duplet rule, whereas Group 17 elements follow the octet rule

OR

Decreasing Order of Atomic Radius:

Rb > K > Na > Li

Increasing Order of Electronegativity (Group 16):

Te < Se < S < O

Decreasing Order of Reducing Power (Group 2):

Ca > Sr > Mg > Be

Electrolytes are classified as strong and weak based on their ability to dissociate into ions when dissolved in water.

Strong Electrolytes: These completely dissociate into ions in solution, resulting in a high concentration of ions. This leads to good electrical conductivity.

• Example: Sodium chloride (NaCl)

Weak Electrolytes: These partially dissociate into ions in solution, resulting in a lower concentration of ions and therefore weaker electrical conductivity.

• Example: Acetic acid (CH₃COOH)

Manufacturing of Nitric Oxide

• Process: Ammonia is oxidized with aerial oxygen to produce nitric oxide.
• Catalyst: Platinum (Pt) catalyst.
• Conditions: 900 °C, 5 – 7 atm

Balanced Chemical Equation

4NH₃ (g) + 5O₂ ​ (g) {{\overset{Pt,\ 800°C, 5 - 7 atm}{\longrightarrow}}} ​ 4NO(g) + 6H₂ ​O(g)

Compounds A and B with the molecular formula C₂H₆O could be:

Compound A

• Name – Ethanol
• Structural formula – CH₃CH₂OH

Compound B

• Name – Dimethyl ether
• Structural formula – CH₃OCH₃

Reaction of A (Ethanol) with Metallic Sodium

2CH₃​CH₂​OH + 2Na → 2CH₃​CH₂​ONa + H₂​(g)

OR

Catalyst Required: Nickel (Ni)

Temperature: 160°C

Balanced Chemical Equation

Ethylene (C₂H₄) reacts with hydrogen (H₂) to form ethane (C₂H₆).

C₂H₄ ​ (g) + H₂ ​ (g) {{\overset{Ni,\ 160 °C}{\longrightarrow}}} ​ C₂H₆ ​ (g)

Compressed Natural Gas (CNG) is commonly used as a fuel for vehicles.

Convection currents are seen in the troposphere.

Two resistances should be connected in parallel.

P₁​ = 1 atm

V_1​ = 150 cm³

P₂​ = 1.5 atm

V₂ = P_1V_1\over P_2

V₂ = 1 × 150\over 1.5 = 100 cm³

The gas will occupy a volume of 100 cm³ at 1.5 atmospheres.

The radioactive ray composed of negatively charged particles is called beta rays (β-rays).

One use of ethylene is in the production of polyethene.

• Semiconductor: Resistivity decreases with increasing temperature.
• Superconductor: Resistivity becomes zero below a critical temperature.

A diverging lens, also known as a concave lens, is a type of lens that is thinner in the middle and thicker at the edges. It causes parallel rays of light to spread out (diverge) after passing through the lens.

When ammonium chloride (NH₄Cl) is heated with dry slaked lime, it undergoes a reaction that produces calcium chloride (CaCl₂), water (H₂O), and ammonia gas (NH₃).

Balanced Chemical Equation:

2NH_4​Cl + Ca(OH)₂​ → CaCl2 ​+ 2H₂​O + 2NH₃​

A saturated hydrocarbon is a type of hydrocarbon in which all carbon-carbon bonds are single bonds. Example – ethane