Madhyamik Class 10 Physical Science Question Paper Solved 2019

c. CH₄ (Methane)

Explanation: Greenhouse gases like methane (CH₄) absorb long-wavelength infrared radiation emitted by the Earth’s surface, trapping heat in the atmosphere.

a. 4.4 g CO₂

Explanation: 

4.4 g CO₂:

Molar mass of CO₂ = 44 g/mol

Moles of CO₂ = 4.4 / 44 = 0.1 mol

Volume = 0.1 × 22.4  = 2.24 L

a. 6.022 × 10²³

c. 3

Explanation: For a solid, there are three types of thermal expansion coefficients:

• Linear expansion coefficient
• Area expansion coefficient
• Volumetric expansion coefficient

c. Infrared ray

b. 15°

Explanation:

The angle of deviation (δ) in refraction is given by the formula:

δ = Angle of incidence − Angle of refraction

Here, the angle of incidence is 45° and the angle of refraction is 30°. So,

δ = 45 ° − 30 ° = 15°

a. V ∝ I

Explanation: Ohm’s Law states that the current (I) flowing through a conductor between two points is directly proportional to the potential difference (V)

V = IR

d. Q = W/V

b. Atomic number increases

Explanation: During β-particle emission (β-decay), a neutron in the nucleus of a radioactive atom is converted into a proton, emitting a β-particle (an electron) and an antineutrino. This process increases the atomic number of the atom by 1.

c. Group 17

Explanation: The halogen elements belong to Group 17 of the long periodic table. They are characterized by having seven electrons in their outermost electron shell.

a. Sodium chloride

Explanation: Sodium chloride (NaCl) is an ionic compound, and its solid state is composed of a regular arrangement of ions (sodium ions and chloride ions) held together by ionic bonds.

c. Liquid HCl

Explanation: Liquid HCl (hydrochloric acid) has the highest ability to conduct electricity among the options given. This is because it is a strong acid that dissociates completely into ions in its liquid state, providing a high concentration of ions that can conduct electricity.

NO

Explanation: During lightning, the high energy breaks the nitrogen (N₂) and oxygen (O₂) molecules in the atmosphere, leading to the formation of nitrogen monoxide (NO). This is a key step in the nitrogen fixation process that converts atmospheric nitrogen into compounds that can be used by living organisms.

c. Al₂O₃.2H₂O

Explanation: Bauxite, the primary ore of aluminium, is commonly represented by the formula Al₂O₃·2H₂O, indicating it is an aluminium oxide hydrate. The specific form of bauxite can vary, but it generally contains aluminium oxide combined with water.

b. Ethyl

Explanation: The ethyl group is the alkyl group containing two carbon atoms. Its formula is C₂H₅.

• Methyl is a one-carbon alkyl group (CH₃).
• Propyl has three carbon atoms (C₃H₇).
• Isopropyl is a branching form of propyl, also containing three carbon atoms.

The unit of calorific value of fuel is Joules per kilogram (J/kg) or kilocalories per kilogram (kcal/kg).

OR

In the stratosphere, the temperature increases with an increase in altitude.

The ozone layer prevents ultraviolet (UV) radiation from reaching the Earth’s surface.

False.

Number of moles = 224\over 22.4 = 10 mole

Mass = Number of moles × Molar mass

= 10 × 28

= 280 grams

False

Explanation: During the conduction of heat through a material, the constituent particles (atoms or molecules) do not change their position. Instead, heat is transferred through the vibration or movement of these particles within their fixed positions.

OR

The relation between thermal resistance (R_th ​) and thermal conductivity (k) of a conductor is given by:

R_th = L/kA

When a ray of light passes through the center of curvature of a concave mirror, the angle of incidence is 0 degrees.

A prism has 3 rectangular surfaces.

Silicon is a common example of a semiconductor.

The thick wire will carry more current when connected to the same potential difference.

Misuse of Nuclear Fission Reaction:

One misuse of nuclear fission reactions is in the creation of nuclear weapons.

OR

The release of a huge amount of energy in nuclear fusion is explained by Einstein’s mass-energy equivalence principle, which is given by the equation:

E=mc²

1. c) Al
2. d) Li
3. a) Cu
4. b) Be

Lewis dot structure of the N₂ molecule

Direct current (DC) electricity is used in electrolysis.

OR

Cathode Reaction in the Electrolysis of Acidulated Water Using Platinum Electrodes:

2H₂O + 2e^– → H₂ + 2OH^–

This reaction produces hydrogen gas at the cathode.

In electroplating gold on brass, the electrolyte used is typically a gold chloride solution or gold cyanide solution.

The reaction of ammonia with Nessler’s reagent forms a yellow or brown colour.

The formula of the precipitate formed when H_₂S gas is passed through an aqueous solution of silver nitrate is Ag₂S (silver sulfide).

OR

The compound formed by the reaction of nitrogen with magnesium metal at a high temperature is magnesium nitride.

The H-C-H bond angle in methane is 109.5°.

OR

The IUPAC name of CH₃CH₂COOH is propanoic acid.

The industrial source of CNG (Compressed Natural Gas) is natural gas, which primarily consists of methane (CH₄).

Sustainable development aims to meet current needs without compromising the ability of future generations to meet theirs. It balances:

1. Environmental Sustainability: Protecting natural resources and ecosystems.
2. Economic Sustainability: Ensuring equitable economic growth.
3. Social Sustainability: Improving quality of life and ensuring social equity.

Pressure (P) = 2 atm

Volume (V) = 410 ml = 0.410 L

Temperature (T) = 7ºC = 280 K

R = 0.082 L atm mol ⁻¹ K ⁻¹

Use the Ideal Gas Law: PV = (m/M) RT

⇒ M = RT\over mPV

⇒ M = 1  × 0.082 × 280\over 2 × 0.410

⇒ M = 28 g/mol

OR

Initial Pressure (P₁)= 1 atm

Initial volume (V₁) = 273 cm³

initial temperature (T₁) = 273 K (STP)

Final volume (V₂) = 300 cm³

Final temperature (T₂) = 300 K

From Combined Gas Equation: P_1V_1\over T_1 = P_2V_2\over T_2

P₂ = P_1V_1T_2\over T_1V_2

P₂ = 1 × 273 × 300\over 273 × 300 = 1 atm

Thus, the pressure is 1 atm.

The refractive index of a medium is a measure of how much the speed of light is reduced when it passes through the medium compared to its speed in a vacuum. It is defined as the ratio of the speed of light in a vacuum (c) to the speed of light in the medium (v):

n = c/v

OR

A convex lens is used to correct hyperopia (farsightedness). In this condition, the eye focuses light behind the retina instead of on it, causing distant objects to be seen more clearly than nearby objects. A convex lens converges the light rays, helping focus them correctly on the retina.

We are given that the current through r₁ ​ is 6 times the current through r₂ ​ when connected to the same potential difference.

Using Ohm’s Law:

I = V/R

Let the current through r₁ ​ be I₁ ​ and through r₂ ​ be  I₂ ​

According to the question,

I₁ = 6 × I₂

⇒ V/r₁ = 6 × V/r₂

⇒ 1/r₁ = 6 × 1/r₂

⇒ r₁/r₂ = 1/6

So, the ratio of r₁ and r₂ is 1 : 6

Kossel explained that an ionic bond forms due to the complete transfer of electrons from one atom (usually a metal) to another atom (usually a non-metal). This process leads to the formation of oppositely charged ions: the metal loses electrons to become a positively charged cation, and the non-metal gains electrons to become a negatively charged anion. The electrostatic attraction between these oppositely charged ions holds them together in an ionic bond.

OR

Liquid Hydrogen Chloride vs Molten Sodium Chloride in Conducting Electricity:

• Liquid hydrogen chloride (HCl) does not conduct electricity because, in its liquid form, HCl consists of neutral molecules. There are no free ions available to carry an electric current.
• Molten sodium chloride (NaCl) can conduct electricity because, when melted, the strong ionic bonds break, and the solid NaCl dissociates into free-moving Na⁺ and Cl⁻ ions. These free ions allow the molten NaCl to conduct electricity as they can move and carry the electric charge.

When ferric chloride reacts with aqueous ammonia, a reddish-brown precipitate of ferric hydroxide (Fe(OH)₃) forms.

Balanced chemical equation

FeCl₃ + 3NH₄OH → Fe(OH)₃ ↓ + 3NH₄Cl

When aluminium chloride (AlCl₃) reacts with aqueous ammonia, a white precipitate of aluminium hydroxide (Al(OH)₃) forms.

AlCl₃ + 3NH₄OH → Al(OH)₃ ↓ + 3NH₄Cl

Zinc blende (ZnS) can be called both a mineral and an ore of zinc because:

• Mineral: Zinc blende is called a mineral because it is a naturally occurring crystalline substance.
• Ore: Zinc blende is also classified as an ore of zinc because zinc can be economically extracted from it.

OR

Two ways to prevent the rusting of iron:

1. Galvanization: Coating iron or steel with a layer of zinc to protect it from rusting.
2. Painting or Coating: Applying a layer of paint or other protective coatings (such as plastic) on the iron surface to create a barrier against moisture and oxygen, thus preventing rust formation.

When methane (CH₄) is burnt in oxygen (O₂), it undergoes a combustion reaction, producing carbon dioxide (CO_₂), and water (H₂O), and releasing energy in the form of heat and light.

Balanced chemical equation

CH₄ ​+ 2O₂ ​→ CO₂ ​+ 2H₂​O

One use of each:

1. Acetic acid: It is used as a key ingredient in vinegar, which is commonly used in cooking and food preservation.
2. Ethyl alcohol (Ethanol): It is used in the preparation of alcoholic beverages.

The molar volume of a gas is the volume occupied by one mole of the gas at standard temperature and pressure.

Two reasons for the deviation are

Balanced Chemical Equation

Fe₂​O_3​ + 2Al → 2Fe + Al₂​O_3​

1 mole   54 g    111.6 g

Calculation of Aluminium

Quantity of Al required to produce 111.6 g of Fe = 54 g

∴ Quantity of Al required to produce 558 g of Fe

= 54\over 111.6 × 558

= 270 g

Calculation of mole of Fe₂O₃

Mole of Fe₂​O_3​ required to produce 111.6 g of Fe = 1 mole

∴ Mole of Fe₂​O_3​ required to produce 558 g of Fe = 1\over 111.6 × 558

= 5

OR

Balanced Chemical Equation:

2NH₄​Cl  + Ca(OH)₂​ → 2NH₃ ​+ CaCl₂ ​+ 2H₂​O

107 g             74 g               34 g       111g

Moles of NH₃ produced

Molar mass of NH₃ = 17 g

Mass of NH₃ = 10.2 g

Moles of NH₃ = 10.2/17 = 0.6

Volume of NH₃ at STP:

Volume = 0.6 × 22.4 = 13.44 L

Mass of Ca(OH)₂ Used:

Molar mass of Ca(OH)₂ = 74 g

From the equation, 1 mole Ca(OH)₂ produces 2 moles NH₃.

So for 0.6 moles NH₃:

Moles of Ca(OH)₂ = 0.6/2 = 0.3 moles

Mass of Ca(OH)₂ = 0.3 × 74 = 11.1 g

Summary

• Mass of Ca(OH)₂ used: 11.1 g
• Moles of NH₃ produced: 0.6 moles
• Volume of NH₃ at STP: 13.44 liters

The volume expansion coefficient (α) of a gas is defined as the fractional change in volume per unit change in temperature at constant pressure. Therefore, the quantity that remains fixed in this definition is:

Pressure (constant pressure is maintained).

Graphite, a form of carbon, is a non-metal that is an excellent conductor of heat.

OR

The linear expansion coefficient of copper, 17 × 10⁻⁶ °C⁻¹, means that for every 1°C rise in temperature, the length of a copper object increases by 17 × 10⁻⁶ times its original length. This describes how much a material expands per degree of temperature change.

A change of 1°C is equal to a change of 1 K, so the rate of expansion per unit temperature change is the same in both scales.

Dentists use a concave mirror.

Refraction of through glass slab:

When a ray of light passes through a glass slab, it undergoes refraction twice: once when entering the glass and once when exiting. The refraction at the second surface is such that the ray emerges parallel to its original path. This happens because the angle of incidence and refraction are equal but opposite at both surfaces, resulting in no overall deviation in the direction of the light ray. However, the ray is displaced laterally.

If no image is obtained when an object is placed 20 cm away from a convex lens, it suggests that the object is at the focus of the lens. This means the object distance (u) is equal to the focal length (f) of the lens. Therefore, the focal length of the lens is:

f = 20 cm

_glassn_air = 1/1.5 = 0.67

Thus, the refractive index of air with respect to glass is 0.67.

OR

The linear magnification ($m$) of a lens is the ratio of the image size to the object size. Given:

• Object length = 5 cm
• Image length = 10 cm

m = Image\ size\over Object\ size = 10\over 5 = 2

So, the linear magnification is 2.

Image Distance:

Magnification (m) = 2

Object distance (u) = – 2 cm

v = m × u = 2 × (-2) = -4 cm

So, the image distance is -4 cm (negative indicating the image is on the same side as the object, meaning it’s a virtual image).

Hydro-electric power generation is based on the principle of converting potential energy of stored water into kinetic energy and then into electrical energy. The basic steps are:

1. Water Storage: Water is stored at a height in reservoirs behind a dam. This water has potential energy due to its elevated position.
2. Water Flow and Turbines: When released, the water flows through pipes (penstocks), and its potential energy is converted into kinetic energy. The flowing water strikes and rotates turbines connected to a generator.
3. Electricity Generation: The rotating turbines drive the generator, converting mechanical energy into electrical energy, which is then distributed for use.

Initial voltage (V₁) = 220 V

Current (I₁) = 1 A

Voltage for the second case (V₂) = 110 V

Resistance (R) of the bulb:

R = V_1\over I_1 = 220\over 1 = 220 Ω

Current in the second case:

I₂ = V_2\over R = 110\over 220 = 0.5 A

OR

The formula for power: P = V^2\over R

For the first bulb (220V-60W):

R₁ = V^2\over P = 220^2\over 60 = 806.67 Ω

For the second bulb (110V-60W):

R₂ = V^2\over P = 110^2\over 60 = 201.67 Ω

Now, find the ratio of their resistances:

Required Ratio = R_1\over R_2 = 806.67\over 201.67 = 4

Thus, the ratio of resistance for the two bulbs is 4:1.

An α-particle consists of 2 protons and 2 neutrons. When emitted, the nucleus loses 2 protons, reducing the atomic number by 2 and the mass number by 4, forming a new element that is two places lower in the periodic table.

γ-ray emission only releases energy without changing the number of protons or neutrons. Since the atomic number remains unchanged, no new element is formed.

Dobereiner’s law of triads states that in a group of three elements (a triad) with similar chemical properties, the atomic mass of the middle element is approximately the arithmetic mean of the atomic masses of the other two elements.

The oxidizing power of these halogens increases as follows:

I < Br < Cl < F

OR

Important Conclusion of Moseley’s Experiment

Moseley’s experiment established that the atomic number (not atomic mass) defines an element’s identity, as X-ray frequencies corresponded to atomic numbers.

Importance of the Periodic Table

This led to the periodic table being organized by atomic number rather than atomic mass, resolving previous inconsistencies and accurately reflecting element properties.

In electrolytic refining of copper, the impure copper rod is used as the anode.

Chemicals Used in Industrial Production of Urea

1. Ammonia (NH₃)
2. Carbon Dioxide (CO₂)

Balanced Chemical Equation

2NH₃ ​ + CO₂ ​ →NH₂ CONH₂ ​+ H₂O

In this reaction, ammonia and carbon dioxide react to form urea and water.

Structural Formulas

(A): Since (A) adds one molecule of bromine per molecule, it must be an alkene with the general formula C₂H4.

The structural formula of (A) is:

Ethene: CH₂ ​=CH₂ ​

(B): Since (B) adds two molecules of bromine per molecule, it must be an alkene with the general formula C₂H₂​.

The structural formula of (B) is:

Ethyne: HC≡CH

Balanced Chemical Equation for (B) with Bromine

HC ≡ CH + 2Br₂ → CHBr₂ − CHBr₂

In this reaction, ethyne reacts with two molecules of bromine to form 1, 2 – dibromoethane

OR

Balanced Chemical Equation:

NaOH + CH₃​COOH → CH₃​COONa + H₂​O

Jute is more environmentally friendly for packaging compared to polythene. This is because jute is a natural, biodegradable fiber that decomposes quickly, while polythene is a synthetic plastic that can take hundreds of years to break down, contributing to environmental pollution.

Solar energy is a non-conventional energy source used to generate electricity.

The SI unit of electric power is the watt (W).

Nitric acid (HNO₃) is manufactured using the catalytic oxidation of ammonia.

Initial volume (V₁ ) = 273 cm³

Initial pressure (P₁) = 1 atm = 760 mm Hg

Initial temperature (T₁) = 273 K (which is 0°C)

Final pressure (P₂) = 76 mm Hg

Final temperature (T₂) = 273°C = 546 K

Apply the Combined Gas Law: P_1V_1\over T_1=P_2V_2\over T_2

⇒ 760 × 273\over 273=76 × V_2\over 546

⇒ V₂ =760 × 273 ×  546\over 273 × 76

⇒ V₂ = 5460 cm³

Thus, the volume of the gas at 76 mm Hg pressure and 273°C is approximately 5460 cm³.

The functional group present in ethyl alcohol (ethanol) is the hydroxyl group (−OH)

A superconductor is a material that can conduct electricity with zero electrical resistance.

Example: Mercury below 4.2 K, and lead below 7.25 are superconductors.

UV rays are used to kill microorganisms in water and on surfaces.

Gamma rays are used in cancer treatment and medical imaging.

One ore of iron is hematite. Its chemical formula is Fe₂O₃.

Polymerisation of ethylene: Ethylene is liquified at high pressure (1500-2000 atm). In the presence of catalysts such as peroxide, oxygen or chromium oxide and at temperatures 150℃-200℃, a large number of ethylene molecules join to form a white solid called polyethylene or polythene.

nC₂​H₄​→(C₂​H₄​​)_n