CBSE EXAMINATION PAPER-2025

In human beings, there are 23 pairs of chromosomes. Out of these 23 pairs of chromosomes (i.e. 46 chromosomes), 22 pairs of chromosomes are called autosomes and one pair of chromosomes. i.e. two chromosomes are called sex chromosomes. The sex chromosomes are of two types — ‘X’ chromosomes and ‘Y chromosomes. The sex of a child (i.e. progeny), is decided at the time of fertilisation. In other words, at the time of zygote formation the sex chromosomes inherited from the parents of a child decide whether the new born will be a boy or a girl.

In order to obtain magnetic field lines around a bar magnet, a student performed an experiment using a magnetic compass and a bar magnet. The magnet was placed on a sheet of white paper fixed on a drawing board. Using magnetic needle he obtained on the paper a pattern of magnetic field lines (as shown below) around the bar magnet.

A common feature observed in the crystals of washing soda, copper sulphate, gypsum and ferrous sulphate is that all:

The values of a, b, c, and d in the following balanced chemical equation are respectively:

a Pb(NO₃)₂ ⟶(heat) b PbO + c NO₂ + d O₂

Which among the following is not a neural action controlled by the part of the human brain labelled ‘X’ in the figure above?

The examples of natural and manmade (artificial) ecosystems are respectively:

Assertion (A): Silver chloride turns grey in sunlight.

Reason (R): Decomposition of silver chloride into silver and chlorine takes place by sunlight.

Assertion (A): The embryo gets nutrition from the mother’s blood with the help of a tissue called placenta.

Reason (R): Placenta is a disc embedded in the uterine wall.

A crystalline substance of green colour ‘X’ emits gases of characteristic odour when heated over a flame. It first loses water and changes colour. On further heating, it decomposes and produces a solid compound Y.

(a) Identify ‘X’ and ‘Y.

(b) State the change in colour observed when ‘X’ is heated.

Give reasons:

(a) The male reproductive organ responsible for formation of germ cells is located outside the abdominal cavity.

(b) The roles of the glands, present along the path of the vas-deferens, are very significant.

How is lymph formed ? State its important function.

(a) Identify ‘X’ in the figure of human nephron shown below. What role does it play in the process of urine formation ?

(b) Why some substances are selectively reabsorbed from the initial filtrate of urine, as it flows along the tabular part of nephron ?

The values of absolute refractive indices of kerosene and water are 1.44 and 1.33 respectively. Compare the two media on the basis of their

(a) optical density

(b) mass density

(c) relative speed of propagation of light.

What do you infer on the basis of above comparisons?

(a) Why are the organisms of first trophic level important in any food chain ?

(b) Justify the following statement :

‘The flow of energy in an ecosystem is unidirectional.’

Establish the relationship between the commercial unit of electric energy and the SI unit of electric energy.

Observe the following diagram showing an experiment to determine the conditions under which a metal ‘M’ corrodes.

List your observations in each of the three cases A, B, and C with reasons, if the metal ‘M’ is generally protected against corrosion by the method of galvanisation.

(a) Write the name and one function of respiratory pigment found in human beings.

(b) Why do lungs always contain a residual volume of air ?

(c) Why is ATP known as energy currency of the living beings ?

(a) Define fertilisation.

(b) What happens to Zygote, Ovule, Ovary and Stamens after fertilisation in a flowering plant ?

The power of a lens is 0.25 D. Based on this information, find out

(a) The type of lens and its focal length.

(b) The eye defect for which it may be used as a corrective lens.

(c) The nature and size of the image formed by this lens when an object is placed between F and 2F from the optical centre of this lens.

(a) “The third wire of earth connection is very important in domestic electric appliances.” Justify this statement.

(b) List two precautions to be taken to avoid the overloading of domestic electric circuits.

(a) Show the formation of Aluminium Nitride (AIN) by the transfer of electrons. [ At. no. of Al = 13; At. no. of N= 7]

(b) “Ionic compounds are solids and are generally brittle and break into pieces when pressure is applied.” Give reason to justify the statement.

(a) What is meant by the term homologous series of carbon compounds ? Write molecular formula of any two consecutive members of homologous series of ketones.

(b) Write chemical equation of the reactions of ethanoic acid with

(i) Sodium hydroxide and

(ii) Ethanol (in the presence of an acid); giving the name of the products in each case.

(c) Draw the structure of the molecule of benzene.

(a) Analyse the given situations and interpret the possible reason for each :

(i) Iodine deficiency in diet increases the possibility of a disease of swollen neck in a person.

(ii) Some people in population may have very short heights (dwarfs).

(iii) Thick facial hairs develop in boys at the age of 10-12 years.

(b) Explain two reasons which necessitate the need of chemical communication in multicellular organisms.

(a) Differentiate between voluntary and involuntary action.

(b) Define reflex action. With the help of a flow diagram, show the correct sequence of path of Nerve impulse from place of its origin.

Analyse the following observation table showing variation of image distance (v) with object distance (u) in case of a convex lens and answer the questions that follow without doing any calculations :

(a) Determine the focal length of the lens. Give reason for your answer.

(b) Find magnification of the image formed in Observation No. 3.

(c) The numerical value of magnifications in cases of observation 1 and 2 is same. List two differences in the images formed in these two cases.