NCERT Solutions Class 9 Science - All 15 Chapters

All 15 Chapters

Matter in Our Surroundings

States of matter, Evaporation, Boiling

› 2

Is Matter Around Us Pure?

Mixtures, Solutions, Separation methods

› 3

Atoms and Molecules

Mole concept, Molecular mass

› 4

Structure of the Atom

Thomson, Rutherford, Bohr model

› 5

The Fundamental Unit of Life

Cell structure, Organelles

› 6

Tissues

Plant and animal tissues

› 7

Diversity in Living Organisms

Classification, Taxonomy

› 8

Motion

Distance, Velocity, Acceleration, Equations of motion

› 9

Force and Laws of Motion

Newton's laws, Momentum

› 10

Gravitation

Newton's law, Weight, Buoyancy

› 11

Work and Energy

Work, Kinetic energy, Potential energy

› 12

Sound

Wave motion, Frequency, Speed of sound

› 13

Why Do We Fall Ill?

Diseases, Immunity, Health

› 14

Natural Resources

Water, Air, Pollution

› 15

Improvement in Food Resources

Crop production, Animal husbandry

›

Chapter 1: Matter in Our Surroundings

Q1. Convert 25°C to Kelvin.

Solution

K = °C + 273 = 25 + 273 = 298 K

Q2. Why does the temperature of a liquid remain constant during boiling?

Solution

During boiling, the heat energy supplied is used to overcome the intermolecular forces of attraction to convert liquid to gas, rather than increasing the kinetic energy (temperature) of molecules.

Chapter 2: Is Matter Around Us Pure?

Q1. What is the difference between a mixture and a compound?

Solution

Mixture: Variable composition, no new substance formed, can be separated physically
Compound: Fixed composition, new substance formed, requires chemical methods to separate

Q2. Define molarity.

Solution

Molarity = Moles of solute / Volume of solution (in litres)

Chapter 3: Atoms and Molecules

Q1. Find the molecular mass of H₂SO₄.

Solution

H: 2 × 1 = 2
S: 1 × 32 = 32
O: 4 × 16 = 64
Total = 98 u

Q2. How many molecules are present in 18 g of water?

Solution

Moles = 18/18 = 1 mol
Molecules = 1 × 6.022 × 10²² = 6.022 × 10²² molecules

Chapter 4: Structure of the Atom

Q1. What is the electronic configuration of sodium (Z = 11)?

Solution

2, 8, 1 or 1s² 2s² 2p⁶ 3s²

Q2. What did Rutherford's alpha particle scattering experiment conclude?

Solution

The experiment concluded that most of the atom is empty space, and the positive charge is concentrated in a small, dense nucleus at the center.

Chapter 5: The Fundamental Unit of Life

Q1. What are the functions of mitochondria?

Solution

Mitochondria are the powerhouses of the cell. They produce ATP energy through cellular respiration.

Q2. What is the difference between plant cell and animal cell?

Solution

Plant cell: Cell wall, chloroplasts, large vacuole
Animal cell: No cell wall, no chloroplasts, small vacuoles, centrioles present

Chapter 8: Motion

Equations of Motion:
• v = u + at
• s = ut + ⅔at²
• v² = u² + 2as

Q1. A car accelerates from 10 m/s to 30 m/s in 5 s. Find the acceleration and distance.

Solution

a = (30-10)/5 = 4 m/s²
s = 10(5) + ⅔(4)(25) = 50 + 50 = 100 m

Q2. What is the SI unit of acceleration?

Solution

m/s² (meter per second squared)

Chapter 9: Force and Laws of Motion

Q1. A 5 kg ball moving at 4 m/s hits a wall and bounces back at 2 m/s. Find the change in momentum.

Solution

∆p = m(v₂ - v₁) = 5(-2 - 4) = -30 kg m/s
Change in momentum = 30 kg m/s

Q2. State Newton's third law of motion with an example.

Solution

For every action, there is an equal and opposite reaction. Example: When you push a wall, the wall pushes you back with equal force.

Chapter 10: Gravitation

• F = Gm₁m₂/r²
• g = GM/R²
• W = mg

Q1. Find the weight of a 10 kg object on Earth (g = 10 m/s²).

Solution

W = mg = 10 × 10 = 100 N

Q2. Why is the weight of an object on the Moon 1/6th of that on Earth?

Solution

Because the gravitational acceleration on the Moon is 1/6th of that on Earth (g_Moon = g_Earth/6), and weight is directly proportional to g.

Chapter 11: Work and Energy

• W = Fs
• KE = ⅔mv²
• PE = mgh
• Power = W/t

Q1. Find the kinetic energy of a 2 kg object moving at 3 m/s.

Solution

KE = ⅔mv² = ⅔ × 2 × 9 = 9 J

Q2. What is the work done in lifting a 5 kg book to a height of 2 m?

Solution

W = mgh = 5 × 10 × 2 = 100 J

Chapter 12: Sound

Q1. What is the speed of sound in air at room temperature?

Solution

Approximately 343 m/s at 20°C

Q2. What is the relationship between frequency, wavelength, and speed of sound?

Solution

v = fλ
Speed = Frequency × Wavelength