CBSE EXAMINATION PAPER-2023
SCIENCE
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 34 questions. All questions are compulsory.
- This question paper is divided into 5 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 21 are very short answer
- Section D – questions number 22 to 29 are short answer
- Section E – questions number 30 to 34 are long 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
(1) State the basis on which the sex of a newborn baby is determined in humans.
[1 Marks](2) Why is the pair of sex chromosomes called a mismatched pair in males?
[1 Marks](3) How is the original number of chromosomes present in the parents restored in the progeny?
[2 Marks](4) Explain by giving two examples of the organisms in which the sex is not genetically determined.
Many optical instruments consist of a number of lenses. They are combined to increase the magnification and sharpness of the image. The net power (P) of the lenses placed in contact is given by the algebraic sum of the powers of the individual lenses P₁, P₂, P₃ … as
P = P₁ + P₂ + P₃ …
This is also termed as the simple additive property of the power of lens, widely used to design lens systems of cameras, microscopes and telescopes. These lens systems can have a combination of convex lenses and also concave lenses.
(1) What is the nature (convergent / divergent) of the combination of a convex lens of power +4 D and a concave lens of power −2 D?
(2) Calculate the focal length of a lens of power −2.5 D.
(3) Draw a ray diagram to show the nature and position of an image formed by a convex lens of power +0.1 D, when an object is placed at a distance of 20 cm from its optical centre.
(4) How is a virtual image formed by a convex lens different from that formed by a concave lens ? Under what conditions do a convex and a concave lens form virtual images ?
Section B
Assertion (A): Human populations show a great deal of variations in traits.
Reason (R): All variations in a species have equal chances of surviving in the environment in which they live.
Assertion (A): The walls of atria are thicker than those of the ventricles.
Reason (R): Ventricles have to pump blood into various organs at high pressure.
Assertion (A): Two magnetic field lines around a current carrying straight wire do not intersect each other.
Reason (R): The magnitude of the magnetic field produced at a given point increases as the current through the wire increases.
Section C
On heating 'X' at 373 K, it loses water molecules and becomes 'Y'. 'Y' is a substance which doctors use for supporting fractured bones in the right position.
(i) Identify 'X' and 'Y'.
(ii) How can 'X' be reobtained from 'Y'?
Two solutions M and N give Red and Blue colour respectively with a universal indicator.
(i) In which solution will the hydrogen ion concentration be more? Justify your answer.
(ii) If both M and N solutions are mixed and the resultant mixture is tested with a universal indicator, it turns green. What is the nature of the salt formed? Justify your answer.
Write the name and function of parts (i) and (ii) in the diagram of a neuron given below.
List the events in proper sequence that take place during the process of photosynthesis.
Explain in brief two ways by which leaves of a plant help in excretion.
In the process of digestion of food in human beings, two protein-digesting enzymes are secreted. Name the enzymes along with the glands that secrete them.
In the given food chain, if 50 J of energy is available to the hawk, how much energy is present at the first and third trophic levels? Justify your answer.
Grass → Grasshopper → Frog → Snake → Hawk
Section D
(a) Define a double displacement reaction.
(b) Write the chemical equation of a double displacement reaction which is also a
(i) Neutralization reaction and
(ii) Precipitation reaction. Give justification for your answer.
(a) Sometimes the pH of our mouth gets lower than 5.5. Why?
(b) A basic salt X' is obtained by heating baking soda followed by crystallisation. Identify 'X' and state its two industrial uses.
(c) Why do copper sulphate crystals turn white on heating?
(i) An object of 5 cm height is placed at a distance of 20 cm from the optical centre of a concave lens of focal length 18 cm. Calculate
(1) image distance and
(2) the magnification in this case.
(ii) Compare the values of magnification obtained by a concave lens and a convex lens when both the lenses form virtual images.
A convex lens can form a
(i) real, inverted and magnified image as well as
(ii) virtual, erect and magnified image of an object. If the focal length of the lens is 10 cm, what should be the range of the object distance in both cases ? Draw ray diagrams to justify your answer.
(a) State one important function of the following parts of the human eye :
(i) Retina
(ii) Pupil
(b) State the role of ciliary muscles in focussing objects at varying distances from the eye.
(i) A straight cylindrical conductor is suspended with its axis perpendicular to the magnetic field of a horse-shoe magnet. The conductor gets displaced towards left when a current is passed through it. What will happen to the displacement of the conductor if the
(1) current through it is increased ?
(2) horse-shoe magnet is replaced by another stronger horse-shoe magnet ?
(3) direction of current through it is reversed?
(ii) Name and state the rule for determining the direction of force on a current carrying conductor in a magnetic field.
Draw the pattern of the magnetic field produced around a vertical current carrying straight conductor passing through a horizontal cardboard. Mark the direction of current and the magnetic field lines. Name and state the rule which is used to determine the direction of magnetic field associated with a current carrying conductor.
How is ozone formed in the higher levels of the atmosphere? "Damage to the ozone layer is a cause of concern." Justify this statement.
Section E
A neutral organic compound ‘X’ (Molecular formula C₂H₆O) on reacting with acidified K₂Cr₂O₇ gives an organic compound ‘Y’ which is acidic in nature. ‘X’ reacts with ‘Y’ on warming in the presence of conc. H₂SO₄ to give a sweet smelling compound ‘Z’.
(i) Identify ‘X’, ‘Y’ and ‘Z’.
(ii) Write the chemical equations for the reactions in the conversion of (1) ‘X’ to ‘Y’ and (2) ‘X’ to ‘Z’.
(iii) State the role of (1) acidified K₂Cr₂O₇ in the conversion of ‘X’ to ‘Y’ and (2) conc. H₂SO₄ in the reaction of ‘X’ and ‘Y’.
(iv) Name the reaction which occurs when ‘Z’ reacts with an alkali.
Carry out the following conversions, stating the condition(s) for each:
(i) Ethanol ⟶ Ethene
(ii) Ethene ⟶ Ethane
(iii) Ethane ⟶ Chloroethane
(iv) Ethanol ⟶ Ethanoic acid
(v) Ethanoic acid ⟶ Ethyl ethanoate
(i) Where are testes located in the human males and why ? State two function of the testes.
(ii) In the human female, one of the ovaries releases an egg every month. State the changes that take place if
(1) the egg is fertilized, and
(2) the egg is not fertilized.
(iii) What is done during the surgical method in males and females to prevent pregnancy ?
(i) What happens when :
(1) Leaves of Bryophyllum fall on the soil ?
(2) Planaria is cut into many pieces ?
(3) Sporangia of Rhizopus on maturation liberate spores ? Mention the modes of reproduction in each of the above three cases.
(ii) Write the changes that occur in a flower once the fertilisation has taken place.
(a) State Ohm’s Law.
(b) Name and define the physical quantity determined by the slope of V–I curve given in the diagram. Use this graph to find the value of this physical quantity in SI units.
(c) Establish the relationship between 1 kWh and 1 joule.
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