Chapter Information

Subject: Science

Class: 9

Practice Set: 2

Question Type: Multiple Choice Questions (MCQs)

Difficulty Level: Moderate

Based On: NCERT Latest Syllabus

Introduction:

Science is the study of the natural world through observation, experimentation, and logical reasoning. Class 9 Science introduces students to important concepts from Physics, Chemistry, and Biology that build a strong foundation for higher classes. Regular practice of concept-based MCQs improves conceptual understanding, analytical thinking, and examination performance.

What You Will Learn?

✔ Acceleration

✔ SI Unit of Force

✔ Sublimation

✔ Mole Concept

✔ Cell Organelles

✔ Scientific Formulae and Facts

✔ NCERT-Based Concepts

✔ Board Exam Preparation

Why This Topic Is Important?

The concepts covered in this practice set are fundamental to Physics, Chemistry, and Biology. They are frequently asked in CBSE, State Board, school examinations, Olympiads, and scholarship tests. Understanding these concepts strengthens scientific reasoning and helps students solve both conceptual and application-based questions with confidence.

Exam Relevance

These questions are useful for:

✔ CBSE Board Exams

✔ State Board Exams

✔ School Tests

✔ Unit Tests

✔ Half-Yearly Exams

✔ Annual Exams

✔ Olympiad Examinations

✔ Scholarship Examinations

Q1. Acceleration is:

1. A) Force
2. B) Change in velocity
3. C) Distance
4. D) Speed

Answer:

Change in velocity

Useful Formula for this Question:

$$a=\frac{v-u}{t}$$

Concept Behind This Question:

Acceleration is the rate at which the velocity of an object changes with time. An object may accelerate when its speed increases, decreases, or its direction changes. According to the NCERT textbook, acceleration is a vector quantity because it has both magnitude and direction.

Step-by-Step Solution:

Acceleration depends on the change in velocity, not simply on speed or distance.

The mathematical relation is:

$$a=\frac{v-u}{t}$$

Where,

• $$a$$ = Acceleration
• $$u$$ = Initial velocity
• $$v$$ = Final velocity
• $$t$$ = Time taken

Since acceleration measures the change in velocity per unit time, the correct answer is:

Change in velocity

Exam Tip:

Do not confuse speed with velocity. Velocity always includes direction, whereas speed does not.

Q2. The SI unit of force is:

1. A) Watt
2. B) Pascal
3. C) Joule
4. D) Newton

Answer:

Newton

Useful Formula for this Question:

$$F=ma$$

Concept Behind This Question:

Force is defined by Newton’s Second Law of Motion. It is the product of the mass of an object and its acceleration. The SI unit of force is the Newton (N).

Step-by-Step Solution:

Using Newton’s Second Law,

$$F=ma$$

Where,

• $$F$$ = Force
• $$m$$ = Mass
• $$a$$ = Acceleration

Among the given options:

• Watt → Unit of Power
• Pascal → Unit of Pressure
• Joule → Unit of Work and Energy
• Newton → Unit of Force

Therefore, the correct answer is:

Newton

Exam Tip:

Remember the SI units:

• Force → Newton
• Work → Joule
• Power → Watt
• Pressure → Pascal

Q3. The change of a solid directly into a gas is called:

1. A) Condensation
2. B) Fusion
3. C) Sublimation
4. D) Evaporation

Answer:

Sublimation

Useful Fact for this Question:

Sublimation is the process in which a solid changes directly into a gas without passing through the liquid state.

Concept Behind This Question:

Certain substances such as camphor, naphthalene, iodine, and ammonium chloride undergo sublimation. This physical change occurs because these substances absorb heat and directly convert into vapour.

Step-by-Step Solution:

Different changes of state are:

• Solid → Liquid = Fusion (Melting)
• Liquid → Gas = Evaporation
• Gas → Liquid = Condensation
• Solid → Gas = Sublimation

Since the question asks about the direct conversion of a solid into a gas, the correct answer is:

Sublimation

Exam Tip:

Remember this sequence:

Solid → Gas = Sublimation

Examples:

• Camphor
• Iodine
• Naphthalene
• Ammonium Chloride

Q4. The mole concept is related to:

1. A) Pressure
2. B) Density
3. C) Number of particles
4. D) Volume

Answer:

Number of particles

Useful Formula for this Question:

$$1\ \text{mole}=6.022\times10^{23}\ \text{particles}$$

Concept Behind This Question:

The mole is the SI unit used to measure the amount of substance. It represents a fixed number of particles such as atoms, molecules, or ions. This fixed number is called Avogadro’s Number and forms the basis of the mole concept in Chemistry.

Step-by-Step Solution:

The mole concept is used to count an extremely large number of particles.

According to NCERT,

$$1\ \text{mole}=6.022\times10^{23}\ \text{particles}$$

Therefore, the mole concept is related to the number of particles, not pressure, density, or volume.

Hence, the correct answer is:

Number of particles

Exam Tip:

Remember Avogadro’s Number:

$$6.022\times10^{23}$$

It is one of the most frequently asked values in Chemistry.

Q5. Which organelle is known as the powerhouse of the cell?

1. A) Vacuole
2. B) Nucleus
3. C) Ribosome
4. D) Mitochondria

Answer:

Mitochondria

Useful Fact for this Question:

Mitochondria produce energy in the form of ATP (Adenosine Triphosphate) through cellular respiration.

Concept Behind This Question:

Every living cell requires energy to perform various life processes such as growth, movement, repair, and reproduction. Mitochondria release this energy by breaking down food molecules, which is why they are called the powerhouse of the cell.

Step-by-Step Solution:

Functions of different cell organelles:

• Vacuole → Storage of water and food materials
• Nucleus → Controls all cellular activities
• Ribosome → Protein synthesis
• Mitochondria → Energy production (ATP)

Therefore, the correct answer is:

Mitochondria

Exam Tip:

Remember:

Mitochondria = ATP Production = Powerhouse of the Cell

Important Formulas & Concepts

1. Formula for Acceleration

$$a=\frac{v-u}{t}$$

Acceleration is the rate of change of velocity with respect to time.

2. Newton’s Second Law of Motion

$$F=ma$$

Where:

• $$F$$ = Force
• $$m$$ = Mass
• $$a$$ = Acceleration

The SI unit of force is Newton (N).

3. Mole Concept

$$1\ \text{mole}=6.022\times10^{23}\ \text{particles}$$

This fixed number is known as Avogadro’s Number.

4. Sublimation

Sublimation is the process in which a solid changes directly into a gas without passing through the liquid state.

Examples:

• Camphor
• Iodine
• Naphthalene
• Ammonium Chloride

5. Mitochondria

Function:

Produces energy in the form of ATP through cellular respiration.

Known as:

Powerhouse of the Cell

FAQs

1. What is acceleration?

Acceleration is the rate of change of velocity with time.

Formula:

$$a=\frac{v-u}{t}$$

2. What is the SI unit of force?

The SI unit of force is Newton (N).

Formula:

$$F=ma$$

3. What is sublimation?

Sublimation is the direct conversion of a solid into a gas without passing through the liquid state.

Examples include camphor, iodine, naphthalene, and ammonium chloride.

4. What does one mole represent?

One mole represents:

$$6.022\times10^{23}$$

particles (atoms, molecules, or ions).

5. Why are mitochondria called the powerhouse of the cell?

Because they produce energy in the form of ATP, which is required for all cellular activities.

Common Mistakes

❌ Confusing speed with velocity.

❌ Writing Joule instead of Newton as the SI unit of force.

❌ Confusing sublimation with evaporation or melting.

❌ Forgetting the value of Avogadro’s Number.

❌ Confusing the nucleus with mitochondria.

Quick Revision Notes

✔ Acceleration Formula:

$$a=\frac{v-u}{t}$$

✔ Force Formula:

$$F=ma$$

✔ SI Unit of Force:

Newton (N)

✔ Solid → Gas = Sublimation

✔ One Mole:

$$1\ \text{mole}=6.022\times10^{23}\ \text{particles}$$

✔ Mitochondria are known as the Powerhouse of the Cell.

✔ Mitochondria produce ATP (Adenosine Triphosphate).

Conclusion

This Class 9 Science MCQ Practice Set 2 covers important concepts from Physics, Chemistry, and Biology based on the latest NCERT syllabus. Topics such as acceleration, force, sublimation, the mole concept, and cell organelles are fundamental for developing a strong understanding of science. Regular practice of these concept-based MCQs helps students improve problem-solving skills, strengthen conceptual clarity, and perform better in CBSE Board Exams, State Board Exams, School Tests, Olympiads, and Scholarship Examinations.