List of top Questions asked in CBSE CLASS XII

Assertion (A): A charged particle is moving with velocity \( v \) in \( x \)-\( y \) plane, making an angle \( \theta \) (\( 0<\theta<90^\circ \)) with \( x \)-axis. If a uniform magnetic field is applied in the region, along \( y \)-axis, the particle will move in a helical path with its axis parallel to \( x \)-axis.
Reason (R): The direction of the magnetic force acting on a charged particle moving in a magnetic field is along the velocity of the particle.

Assertion (A): A ray of light is incident normally on the face of a prism. The emergent ray will graze along the opposite face of the prism when the critical angle at glass-air interface is equal to the angle of the prism.
Reason (R): The refractive index of a prism depends on angle of the prism.

Assertion (A): EM waves do not require a medium for their propagation.
Reason (R): EM waves are transverse waves.

Out of the four options given, in which transition will the emitted photon have the maximum wavelength?

The frequency of a photon of energy 1.326 eV is:

The effective resistance between points A and B in the given circuit is:

The dimensional formula of magnetic permeability \(\mu_0\) is:

A capacitor and an inductor are connected in series across an ac source of voltage of variable frequency. The frequency is increased continuously. The nature of the circuit before and after the resonance will be:

An alternating current is given by \( I = I_0 \cos (100\pi t) \). The least time the current takes to decrease from its maximum value to zero will be:

A metal rod of length 50 cm is held vertically and moved with a velocity in a magnetic field at the place of 0.4 G. The emf induced across the ends of the rod is:

A rectangular coil of area A is kept in a uniform magnetic field \(\vec{B}\) such that the plane of the coil makes an angle \(\alpha\) with \(\vec{B}\). The magnetic flux linked with the coil is:

Two horizontal plates, separated by 1 cm, are arranged one above the other. A particle of mass 5 mg and charge 2 nC is released in air between the plates. The potential difference that should be applied to the plates so that the particle remains suspended between them is:

Given below are few statements with respect to the process of oogenesis in a human ovary:
(i) Each granulosa cell gets surrounded by a primary oocyte to form the primary follicle.
(ii) A couple of million of oogonia are formed within each fetal ovary during the embryonic development.
(iii) Tertiary follicle is characterised by antrum and theca layers.
(iv) Secondary follicles form a zona pellucida layer around it.
(v) Mature graafian follicle ruptures to release the secondary oocyte from the ovary.
Choose the option with all true statements from the given options:

Thomas Hunt Morgan carried out several dihybrid crosses in Drosophila melanogaster to study genes that were sex linked.
(a) Give four major reasons for using the tiny fruit flies by Morgan for his experiments.
(b) How did Morgan and his group explain the physical association of the two genes on a chromosome to the frequency of recombination between gene pairs on the same chromosome?

Answer either option-(A) or (B): (A)

Name the two genes encoding for the Bt toxin protein used in biotechnology for the control of cotton bollworms.
How does the expression of Bt toxin gene in Bt cotton plant help in providing resistance to cotton bollworms? Explain.

OR (B)

Explain the given methods of introducing the alien DNA in the host cells:
(I) Biolistics
(II) Microinjection
How is E. coli made 'competent' to take up a recombinant plasmid or DNA?

Student to attempt either option (A) or (B):
(A) Write two features of an ideal contraceptive. Explain any one natural contraceptive method that makes the chances of conception almost nil.
OR
(B) Explain GIFT and ICSI.

Student to attempt either option (A) or (B):
(A) Explain how the immunity of a person is affected if there is atrophy (degeneration) of the thymus gland at an early stage of life.
OR
(B) (i) What are interferons? Explain their role in providing immunity to a person.
(ii) Which category of innate immunity defence barrier can interferons be classified into?

Large holes in 'Swiss cheese' are formed by the activity of microbes:

Early detection of HIV in suspected AIDS patients can be done using the diagnostic technique of:

The primates that probably lived in East Africa grasslands about two mya were:

The simplest definition of a gene in eukaryotes is --- A unit of DNA that has information to mainly specify the synthesis of:

A colourblind man marries a woman with normal sight who has no history of colourblindness in her family. What is the probability of their son being colourblind?

Select the statements that are true for a typical megasporangium of flowering plants:
(i) It is attached to the placenta by hilum.
(ii) It has a chalaza end that represents the basal part of the ovule.
(iii) It has nucellus enclosed by integuments.
(iv) Its micropylar end is known as chalaza.
Choose the correct answer:

The type of antibodies produced during an immune response to allergens as dust and pollen grains in a person is:

Assertion (A): The meristems are grown ‘in vitro’ to obtain virus-free plants from an infected plant.
Reason (R): If the plant is infected with a virus, the roots and the stems are free of virus.