CBSE EXAMINATION PAPER-2023
SCIENCE
(Solved)
General Instructions :
Read the following instructions carefully and follow them :
- This question paper contains 37 questions. All questions are compulsory.
- This question paper is divided into 5 sections.
- Section A – questions number 1 to 3 are case based questions
- Section B – questions number 4 to 17 are multiple choice questions
- Section C – questions number 18 to 25 are very short answer
- Section D – questions number 26 to 33 are short answer
- Section E – questions number 34 to 37 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
On the basis of reactivity metals are grouped into three categories -
(i) Metals of low reactivity
(ii) Metals of medium reactivity
(iii) Metals of high reactivity
Therefore metals are extracted in pure form from their ores on the basis of their chemical properties.
Metals of high reactivity are extracted from their ores by electrolysis of the molten ore.
Metals of low reactivity are extracted from their sulphide ores, which are converted into their oxides. The oxides of these metals are reduced to metals by simple heating.
(1) Name the process of reduction used for a metal that gives vigorous reaction with air and water both.
(2) Carbon cannot be used as a reducing agent to obtain aluminium from its oxide? Why?
(3) Describe briefly the method to obtain mercury from cinnabar. Write the chemical equation for the reactions involved in the process.
(4) Differentiate between roasting and calcination giving chemical equation for each.
All human chromosomes are not paired. Most human chromosomes have a maternal and a paternal copy, and we have 22 such pairs. But one pair called the sex chromosomes, is odd in not always being a perfect pair. Women have a perfect pair of sex chromosomes. But men have a mismatched pair in which one is normal sized while the other is a short one.
(1) In humans, how many chromosomes are present in a Zygote and in each gamete?
(2) A few reptiles rely entirely on environmental cues for sex determination. Comment.
(3) "The sex of a child is a matter of chance and none of the parents are considered to be responsible for it." Justify it through flow chart only.
(4) Why do all the gametes formed in human females have an X chromosome?
A student took three concave mirrors of different focal lengths and performed the experiment to see the image formation by placing an object at different distances with these mirrors as shown in the following table.
(1) List two properties of the image formed in Case I.
(2) In which one of the cases given in the table, the mirror will form real image of same size and why?
(3) Name the type of mirror used by dentists. Give reason why do they use such type of mirrors.
(4) Look at the table and identify the situation (object distance and focal length) which resembles the situation in which concave mirrors are used as shaving mirrors? Draw a ray diagram to show the image formation in this case.
Section B
Metal oxides generally react with acids, but few oxides of metal also react with bases. Such metallic oxides are :
I. MgO
II. ZnO
III. Al₂O₃
IV. CaO
In the given diagram of a closed stomata (1), (2), (3) and (4) respectively are
Walking in a straight line and riding a bicycle are the activities which are possible due to a part of the brain. Choose the correct location and name of this part from the given table:
A student wants to obtain an erect image of an object using a concave mirror of 10 cm focal length. What will be the distance of the object from mirror?
Bronze is an alloy of
In an experiment with pea plants, a pure tall plant (TT) is crossed with a pure short plant (tt). The ratio of pure tall plants to pure short plants in F₂ generation will be —
Choose the correct order of the stages of binary fission in Leishmania.
Section C
State whether the given chemical reaction is a redox reaction or not. Justify your answer.
MnO₂ + 4 HCl → MnCl₂ + 2 H₂O + Cl₂
List two differences between the movement of leaves of a sensitive plant and the movement of a shoot towards light.
What happens at synapse between two neurons? State briefly.
Give the name of the enzyme present in the fluid in our mouth cavity. State the gland which produces it. What would happen to the digestion process if this gland stops secreting this enzyme?
Let the resistance of an electrical device remain constant, while the potential difference across its two ends decreases to one fourth of its initial value. What change will occur in the current through it? State the law which helps us in solving the above stated question.
A light ray enters from medium A to medium B as shown in the figure.
(a) Which one of the two media is denser w.r.t. other medium? Justify your answer.
(b) If the speed of light in medium A is vₐ and in medium B is vᵦ, what is the refractive index of B with respect to A?
(a) A ray of light starting from diamond is incident on the interface separating diamond and water. Draw a labelled ray diagram to show the refraction of light in this case.
(b) Absolute refractive indices of diamond and water are 2.42 and 1.33 respectively. Find the value of refractive index of water w.r.t. diamond.
State the rule to determine the direction of a (a) magnetic field produced around a straight conductor carrying current and (b) force experienced by a current carrying straight conductor placed in a magnetic field which is perpendicular to it.
Section D
Explain the process of transport of oxygenated and deoxygenated blood in a human body.
A substance 'X' is used as a building material and is insoluble in water. When it reacts with dilute HCl, it produces a gas which turns lime water milky.
(i) Write the chemical name and formula of 'X'.
(ii) Write chemical equations for the chemical reactions involved in the above statements.
A metal 'M' on reacting with dilute acid liberates a gas 'G'. The same metal also liberates gas 'G' when reacts with a base.
(i) Write the name of gas 'G'.
(ii) How will you test the presence of this gas?
(iii) Write chemical equations for the reactions of the metal with
(1) an acid and (2) a base.
Name the gland and the hormone secreted by it in scary situations in human beings. List any two responses shown by our body when this hormone is secreted into the blood.
In the given diagram
(1) Name the parts labelled A, B, and C.
(ii) Write the functions of A and C.
(iii) Reflex arcs have evolved in animals? Why?
With the help of an appropriate example, justify that some of the chemical reactions are determined by
(a) Change in temperature,
(b) Evolution of a gas, and
(c) Change in colour
Give chemical equation for the reaction involved in each case.
State reasons for Myopia. With the help of ray diagrams, show the
(a) image formation by a myopic eye, and
(b) correction of myopia using an appropriate lens.
(a) Write the percentage of (i) solar energy captured by the autotrophs and (ii) energy transferred from autotrophs to the next level in a food chain.
(b) What are trophic levels? Why do different food chains in an ecosystem not have more than four to five trophic levels? Give reason.
Section E
(i) A compound ‘A’ with a molecular formula of C₂H₄O₂ reacts with a base to give salt and water. Identify ‘A’, state its nature and the name of the functional group it possesses. Write the chemical equation for the reaction involved.
(ii) When the above stated compound ‘A’ reacts with another compound ‘B’ having molecular formula C₂H₆O in the presence of an acid, a sweet-smelling compound ‘C’ is formed.
(1) Identify ‘B’ and ‘C’.
(2) State the role of acid in this reaction.
(3) Write the chemical equation for the reaction involved.
(i) Name the compound formed when ethanol is heated at 443 K in the presence of conc. H₂SO₄ and draw its electron-dot structure. State the role of conc. H₂SO₄ in this reaction.
(ii) What is hydrogenation? Explain it with the help of a chemical equation. State the role of this reaction in industry.
(i) What is meant by resistance of a conductor? Define its SI unit.
(ii) List two factors on which the resistance of a rectangular conductor depends.
(iii) How will the resistance of a wire be affected if its
(1) length is doubled, and
(2) radius is also doubled?
Give justification for your answer.
In an electric circuit three bulbs of 100 W each are connected in series to a source. In another circuit set of three bulbs of the same wattage are connected in parallel to the same source.
(i) Will the bulb in the two circuits glow with the same brightness? Justify your answer.
(ii) Now, let one bulb in both the circuits get fused. Will the rest of the bulbs continue to glow in each circuit? Give reason for your answer.
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