CBSE EXAMINATION PAPER-2024
SCIENCE
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 24 questions. All questions are compulsory.
- This question paper is divided into 4 sections.
- Section A – questions number 1 to 2 are case based questions
- Section B – questions number 3 to 14 are multiple choice questions
- Section C – questions number 15 to 20 are very short answer
- Section D – questions number 21 to 24 are short answer
- There is no overall choice given in the question paper. However, an internal choice has been provided in few questions.
- Use of calculator is NOT allowed.
Section A
Mendel worked out the rules of heredity by working on garden pea using a number of visible contrasting characters. He conducted several experiments by making a cross with one or two pairs of contrasting characters of pea plant. On the basis of his observations he gave some interpretations which helped to study the mechanism of inheritance.
(1) When Mendel crossed pea plants with pure tall and pure short characteristics to produce F₁ progeny, which two observations were made by him in F₁ plants?
(2) Write one difference between dominant and recessive trait.
[1 Marks](3) In a cross with two pairs of contrasting characters Mendel observed 4 types of combinations in F₂ generation. By which method did he obtain F₂ generation? Write the ratio of the parental combinations obtained and what conclusions were drawn from this experiment.
[2 Marks]
(4) Justify the statement: "It is possible that a trait is inherited but may not be expressed."
(1) List two properties of the image formed in case 2.
[1 Marks](2) In which one of the above cases will the mirror form a diminished image of the object? Justify your answer.
[1 Marks](3) What is the nature and size of the image formed by mirror C? Draw a ray diagram to justify your answer.
[2 Marks](4) An object is placed at a distance of 18 cm from the pole of a concave mirror of focal length 12 cm. Find the position of the image formed in this case.
Section B
A metal and a non-metal that exists in liquid state at the room temperature are respectively:
Carbon compounds:
(i) are good conductors of electricity.
(ii) are bad conductors of electricity.
(iii) have strong forces of attraction between their molecules.
(iv) have weak forces of attraction between their molecules.
The correct statements are:
Consider the following compounds:
FeSO₄, CuSO₄, CaSO₄, Na₂CO₃
The compound having maximum number of waters of crystallization in its crystalline form in one molecule is:
MnO₂+4HCl→MnCl₂+2H₂O+ Cl₂.
The reaction given above is a redox reaction because in this case:
Chromosomes:
(i) carry hereditary information from parents to the next generation.
(ii) are thread-like structures located inside the nucleus of an animal cell.
(iii) always exist in pairs in human reproductive cells.
(iv) are involved in the process of cell division. The correct statements are:
Section C
Explanation: When calcium oxide (CaO) reacts with water (H2O), they combine to form a single product, calcium hydroxide Ca(OH)2, also known as slaked lime. This type of reaction where two or more reactants combine to form one product is called a combination reaction.
Chemical Equation: CaO (s) + H2O (l) → Ca(OH)2 (aq) + Heat
This reaction releases heat, which shows it is exothermic. It is also called the slaking of lime.
How is the movement of leaves of a sensitive plant different from the downward movement of the roots?
There is a hormone which regulates carbohydrate, protein and fat metabolism in our body. Name the hormone and the gland which secretes it. Why is it important for us to have iodised salt in our diet?
In the given circuit calculate the power consumed in watts in the resistor of 2 Ω:
(i) Two magnetic field lines do not intersect each other. Why?
(ii) How is a uniform magnetic field in a given region represented? Draw a diagram in support of your answer.
(i) Two magnetic field lines do not intersect each other because if they did, it would mean that at the point of intersection, the magnetic field has two different directions, which is not possible. The tangent to the field line at any point shows the direction of the magnetic field, so field lines must not cross.
(ii) A uniform magnetic field is represented by straight, parallel, and equally spaced magnetic field lines. This shows that the magnetic field has the same strength and direction at every point in that region. For example, between two opposite poles of two identical magnets placed close to each other, the magnetic field lines are parallel and evenly spaced.
Section D
(i) The pH of a sample of tomato juice is 4.6. How is this juice likely to be in taste? Give reason to justify your answer.
(ii) How do we differentiate between a strong acid and a weak base in terms of ion-formation in aqueous solutions ?
(iii) The acid rain can make the survival of aquatic animals difficult. How?
(ii) A strong acid ionizes completely in aqueous solution, producing a large number of H+ ions. For example, hydrochloric acid (HCl) dissociates fully to give H+ and Cl- ions. A weak base, on the other hand, does not ionize completely in water and produces fewer OH- ions. For example, ammonia (NH3) ionizes partially, forming fewer hydroxide ions. Thus, ion formation helps differentiate between strong acids and weak bases.
(iii) Acid rain contains dissolved acidic components like sulfuric and nitric acids which lower the pH of water bodies. This acidic environment harms aquatic animals by disrupting their physiological balance, damaging gills, causing skin irritation, and affecting reproduction. Low pH can also dissolve toxic metals from the soil which further pollute the water and make survival difficult for aquatic life.
A gas 'X' which is a deadly poison is found at the higher levels of the atmosphere and performs an essential function.
Name the gas and write the function performed by this gas in the atmosphere. Which chemical is linked to the decrease in the level of this gas? What measures have been taken by an international organization to check the depletion of the layer containing this gas?
The gas 'X' referred to in the question is ozone (O₃). Although ozone is a deadly poison at ground level, it plays a crucial role in the higher levels of the atmosphere, specifically in the ozone layer. It absorbs and shields the Earth's surface from harmful ultraviolet (UV) radiation from the Sun, which can cause serious health problems such as skin cancer and damage to living organisms.
The depletion of the ozone layer is mainly caused by chemicals called chlorofluorocarbons (CFCs). These chemicals release chlorine atoms when they break down in the stratosphere, which then destroy ozone molecules, leading to thinning of the ozone layer.
To address this serious environmental problem, the international community adopted the Montreal Protocol, an agreement to phase out the production and use of ozone-depleting substances like CFCs. Due to these measures, the ozone layer's depletion has slowed down, and there are signs of recovery, although continuous efforts are needed to protect it fully.
Name and state the rule to determine the direction of a:
(i) magnetic field produced around a current carrying straight conductor.
(ii) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
(i) The rule to determine the direction of the magnetic field around a current-carrying straight conductor is called the Right-Hand Rule. According to this rule, if you point the thumb of your right hand in the direction of the current, then the way your fingers curl around the conductor shows the direction of the magnetic field. This magnetic field forms concentric circles around the wire.
(ii) The rule to find the direction of the force on a current-carrying conductor placed in a magnetic field perpendicular to it is called Fleming's Left-Hand Rule. According to this rule, stretch your thumb, first finger, and second finger of the left hand so that they are mutually perpendicular. The first finger points in the direction of the magnetic field (from North to South), the second finger points in the direction of the current, and the thumb will then point in the direction of the force (motion) experienced by the conductor.
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