# HBSE Class 9 Science Question Paper 2024 Answer Key

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HBSE Class 9 Science Question Paper 2024 Answer Key

Section – A (Physics)

1. Inertia is the property of a body by virtue of which, it cannot change by itself : (1 Mark)
(a) Its direction of motion
(b) Its steady state of uniform motion
(c) Its state of rest
(d) All of these
Answer – (d) All of these

2. The question below consists of two statements : (1 Mark)
Assertion (A) : The cork floats while nail sinks in the water.
Reason (R) : This happens because of the difference in their densities.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true and R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Answer – (a) Both A and R are true and R is the correct explanation of A.

3. Mass of an object is 10 kg. What is its weight on the earth? (1 Mark)
(a) 98 kg
(b) 9.8 kg
(c) 10 kg
(d) 98 N
F = mg = 10 × 9.8 = 98 Newton

4. Which form of energy does the flowing water possess? (1 Mark)
(a) Potential energy
(b) Kinetic energy
(c) Electrical energy
(d) Gravitational energy

5. The sound which is produced due to a mixture of several frequencies is called a …………….. and is pleasant to listen. (1 Mark)

6. A racing car has a uniform acceleration of 4 ms-². What distance will it cover in 10 second after start? (2 Marks)
Answer – Using second equation of motion,
Distance (s) = ut + ½at²
s = 0×10 + ½(4)(10)²
s = 200 m

7. Define average speed. Write its formula. (2 Marks)
Answer – Average speed is a rate that is a quantity divided by the time taken to get that quantity. SI unit of speed is meters per second (m/s).
Avg. speed = Total Distance/Total Time

OR

Define acceleration. Write its formula.
Answer – Acceleration can be defined as the rate of change of velocity with time. It can also be defined as the increase in velocity per second. The S.I. unit of acceleration is meter per second square (m/s² or ms-²).

8. Distinguish between loudness and intensity of sound. (2 Marks)
Answer : Loudness – Loudness is a measure of the response of the ear to the sound. The loudness of a sound is defined by its amplitude.
• Intensity of a sound – Intensity of a sound wave is defined as the amount of sound energy passing through a unit area per second.

9. Why do you fall in the forward direction, when a moving bus brakes to stop and fall backwards, when it accelerates from rest? (3 Marks)
Answer – When a moving bus breaks to stop we fall in the forward direction Due to inertia of Motion and when the bus accelerates from rest we fall in the backward direction Due to inertia of Rest.

10. Define the following with unit : (3 Marks)
(i) Potential energy
Answer – Potential energy is the energy that is stored in an object due to its position or configuration. In other words, potential energy refers to the energy which an object holds due to its position relative to other objects, stresses within itself, its electric charge, or other factors.

(ii) Power
Answer – We can define power as the Rate of doing work. It is equivalent to an amount of energy consumed per unit time. The SI unit of power is watt (W).

OR

Calculate the work required to be done to stop a car 1500 kg moving at a velocity of 60 km/h.
Answer – Here velocity (v) = 60 km/h = 50/3 m/s
Work (K.E) = ½mv² = ½ × 1500 × (50/3)² = 208333.334 J = 208.33 kJ

11.(a) How does the force of gravitation between two objects change when the distance between them is reduced to half? (2 Marks)
Answer – Gravitational force (F) = Gm1m2/r²
New force (F’) = Gm1m2/(r/2)² = 4 Gm1m2/r²
so, F’ = 4F
Hence, when the distance between the objects is reduced to half, the gravitational force increases four times.

(b) Write the three importance of Universal Law of Gravitation. (3 Marks)
Answer – The importance of the universal law of gravitation is as follows :
(i) It explains the motion of planets around the sun.
(ii) It helps in determining the trajectory of astronomical bodies and to predict their motion. (iii) It also explains the phenomena of rainfall, snowfall, and flow of water in rivers on the earth.

OR

(a) Why is it difficult to hold a school bag having a strap made of a thin and strong string? (2 Marks)
Answer – It is difficult to hold a school bag having a thin strap because the pressure on the shoulders is quite large. This is because the pressure is inversely proportional to the surface area on which the force acts. The smaller is the surface area; the larger will be the pressure on the surface.

(b) A ball thrown up vertically returns to the thrower after 6 second. (3 Marks)
Find :
(i) The velocity with which it was thrown up.
Answer – Maximum height time = 6/2 = 3 s
v = u + at
0 = u + (-10)×3
u = 30 m/s
The velocity with which it was thrown up is 30 m/s.

(ii) The maximum height it reaches.
Answer – Using formula, s = ut + ½at²
h = 30×3 + ½(-10)(3)²
h = 45 m
The maximum height it reaches is 45 m.

(iii) Its position after 4 second.
Answer – Using formula, s = ut + ½at²
d = 0 + ½(10)(1)²
d = 5 m
Its height above the ground is 45m – 5m = 40m.
Hence after 4s, the ball is at a height of 40 m above the ground.

Section – B (Chemistry)

12. The temperature at which a solid melts to become a liquid at the atmospheric pressure is called its …………… . (1 Mark)

13. When the liquid is spun rapidly, the denser particles are forced to the bottom and the lighter particles stay at the top. This principle is used in : (1 Mark)
(a) Evaporation
(b) Chromatography
(c) Centrifugation
(d) Fractional distillation

14. Which of the following is physical changes? (1 Mark)
(a) Dissolving common salt in water.
(b) Melting of butter in a pan.
(c) Boiling of water to form steam.
(d) All of these
Answer – (d) All of these

15. Write chemical formula of Carbon tetrachloride. (1 Mark)

16. If K and L shells of an atom are full, then what would be the total number of electrons in the atom? (1 Mark)
(a) 2
(b) 8
(c) 10
(d) 18
The maximum number of electrons in first orbit (K shell) will be 2 × 1² = 2 and the maximum number of electrons in second orbit (L shell) will be 2 × 2² = 8. Hence, if K and L shell is full, the total number of electrons in the atom will be 2 + 8 = 10.

17. Write two differences between mixture and compound. (2 Marks)

 Mixture Compund 1. The mixture is the physical combination of substances, bonded together in any proportion. 1. The compound is the chemical combination of elements, bonded together in specific proportion. 2. The mixture is an impure substance. 2. The compound is a pure substance. 3. Example: sand and water. 3. Example: water and carbon dioxide.

18. What do you mean by Isotopes? Write one example of Isotopes. (2 Marks)
Answer – The atoms of the same element which have the same atomic number Z but different mass number A are called isotopes. For example, there are three isotopes of Hydrogen are Protium (1H¹), Deuterium (1H²) and Tritium (1H³).

OR

Write the distribution of electrons in Nitrogen and Magnesium.
Answer – Atomic number of nitrogen is 7. Its electronic distribution is (2,5).
Atomic number of magnesium is 12. Its electronic distribution is (2,8,2).

19.(a) What will be the physical state of water at 25°C ? (1 Mark)

(b) Why are we able to sip hot tea or milk faster from a saucer rather than a cup? (2 Marks)
Answer – We are able to sip tea or milk faster from a saucer because it has a larger surface area than the cup. In larger surface area rate of evaporation is faster due to which tea or milk cools rapidly.

20. If bromine atom is available in the form of, say, two isotopes [35Br⁷⁹(49.7%)] and [35Br⁸¹(50.3%)], calculate the average atomic mass of bromine atom. (3 Marks)
Answer – Average atomic mass of bromine atom = [(atomic mass of 35Br⁷⁹ × percentage) + (atomic mass of 35Br⁸¹ × percentage)] ÷ 100
Avg. atomic mass of bromine atom = (79 × 49.7/100) + (81 × 50.3/100) = 80.006 u

21.(a) Write down the names of compounds represented by the following formulae : (3 Marks)
(i) Al2(SO4)3

(ii) K2SO4

(iii) CaCO3

(b) What are polyatomic ions? Give examples. (2 Marks)
Answer – The ions which contain more than one atoms behaving as a single unit are called polyatomic ions. For example, nitrate ion NO3-, contains one nitrogen atom and three oxygen atoms.

OR

(a) Explain with examples : (3 Marks)
(i) Mass number
Answer – The total number of protons and neutrons present in the nucleus of an atom is called the mass number.

(ii) Isobars
Answer – Isobars are the atoms of different elements having a different atomic number but the same mass number are called isobars.

(b) If number of electrons in an atom is 8 and number of protons is also 8, then : (2 Marks)
(i) What is the atomic number of the atom?
Answer – The atomic number is equal to the number of protons. Therefore, the atomic number of the atom is 8.

(ii) What is the charge on the atom?
Answer – Since the number of both electrons and protons is equal, therefore, the charge on the atom is Zero.

Section – C (Biology)

22. Which organelle is known as the powerhouse of the cell? (1 Mark)

23. Which tissue makes up the husk of coconut? (1 Mark)
(a) Parenchyma tissue
(b) Collenchyma tissue
(c) Sclerenchyma tissue
(d) All of these

24. Nervous tissue is made of ……………… that receive and conduct impulses. (1 Mark)

25. Which of the following are finned fish? (1 Mark)
(a) Mullet
(b) Bhetki
(c) Pearlspots
(d) All of these
Answer – (d) All of these

26. Growing two or more crops in definite row patterns is known as …………… (1 Mark)
(a) Crop rotation
(b) Inter-cropping
(c) Mixed cropping
(d) Mixed farming system

27. Write two common management practices of animal husbandary and poultry farming. (2 Marks)
Answer – Common practice in dairy and poultry farming are :
(i) Proper shelter facilities and their regular cleaning.
(ii) Some basic hygienic conditions such as clean water, nutritious food, etc.
(iii) Animals are kept in spacious, airy and ventilated places.

28. Why are Lysosomes known as ‘suicide bags’? (3 Marks)
Answer – If the cell gets damaged, then one of the lysosomes bursts and release some digestive enzymes. The released enzymes then digest their own cell and ultimately the cell dies. Hence, lysosomes are called suicide bags of the cell.

29. Draw a well labelled diagram of a plant cell. (3 Marks)

OR

Write three differences between plant cell and animal cell.

 Plant Cells Animal Cells 1. Have a rigid cell wall made of cellulose that surrounds the cell membrane, providing structural support and shape. 1. Lack a cell wall; they only have a flexible cell membrane, allowing for a variety of cell shapes. 2. Contain chloroplasts, which are the sites of photosynthesis and contain chlorophyll, the pigment that captures light energy. 2. Do not have chloroplasts and do not perform photosynthesis. 3. Generally have a fixed, rectangular shape due to the rigid cell wall. 3. Tend to have a more irregular, rounded shape due to the absence of a cell wall. 4. Store energy primarily in the form of starch. 4. Store energy in the form of glycogen.

30.(a) How many types of elements together makeup the xylem tissue? Name them. (2 Marks)
Answer – They are four type : Tracheids, Vessels, Xylem parenchyma and Xylem fibres.

(b) Write three functions of Areaoler tissue. (2 Marks)
Answer – Functions of areaoler tissue are :
(i) It provides support and helps to protect organs, muscles, and many other tissues.
(ii) It also helps to bind the skin together.
(iii) Provides a protective framework that keeps major structures in place and offers support.
(iv) Contains mast cells that help prevent infection.

OR

(a) Draw a well labelled diagram of neuron. (2 Marks)