List of top Questions asked in CBSE CLASS XII

Name the process involved in the production of nematode-resistant tobacco plants, using genetic engineering. Explain the strategy adopted to develop such plants.
Answer the following questions:
  • Write the scientific name of the fruit fly.
  • Why did Morgan prefer to work with fruit flies for his experiments? State two reasons.
Student to attempt either option (A) or (B): (A) Biotechnology has helped farmers to get pest-resistant cotton plants. Explain the technique adopted along with its mode of action.
OR
(B) Explain any two molecular diagnostic techniques that help to detect pathogens from suspected patient.
Assertion (A): Human male is referred to as heterogametic.
Reason (R): The male produces millions of sperms of the same kind.

Study the table given below showing the relationship between organism, its trophic level and kind of food chain it belongs to.

Name the microbe that is used as biocontrol agent for controlling pest butterfly caterpillars:
A dwarf pea plant was treated with gibberellic acid and it becomes as tall as a tall pea plant. If these treated pea plants are crossed with pure tall pea plants, the phenotypic ratio in $F_1$ generation will be:
During the process of oogenesis in human female, the primary oocyte results in the formation of which of the following?
Choose the correct option.
pBR which is frequently used as a vector for cloning gene in E. coli is a/an:
In Bohr model of hydrogen atom, an electron is revolving in second orbit. Find the value of:
(i) angular momentum of electron,
(ii) radius of the orbit, and
(iii) kinetic energy of electron.
Take radius of first orbit of hydrogen atom as 0.5 \AA.
State Kirchhoff’s laws. Apply these laws to find the values of current flowing in the three branches of the given circuit.
Kirchhoff’s laws.
A concave mirror has a radius of curvature 20 cm. Calculate the distance of an object from the mirror so as to form an image of magnification -2. Also, find the location of the image.
Differentiate between ‘nuclear fission’ and ‘nuclear fusion’. Briefly discuss one example of each.
A tank is filled with a liquid of refractive index \( \sqrt{2} \), up to a height of 30 cm. A tiny bulb is glowing at the bottom of the tank. Calculate the diameter of an opaque disc floating symmetrically on the liquid surface that can cut off completely the light from the bulb that comes out of the liquid surface.
An alpha particle and a deuterium ion are accelerated through the same potential difference. These are then directed towards a target nucleus to make a head-on collision. It is observed that their distance of closest approach is the same. Justify it theoretically.
What is the difference between ‘velocity’ and ‘drift velocity’ of electrons in a current-carrying conductor.
The wavelength of a photon is equal to the wavelength associated with an electron. Both will have the same value of:
A particle of mass \( m \) and charge \( q \) moving with velocity \( \vec{v} = v \hat{i} \) is subjected to a uniform electric field \( \vec{E} = E \hat{j} \). The particle will initially have a tendency to move in a circle of radius:
The ratio of potential difference across AB in the circuit shown for the case (i) when switch S is closed and (ii) when S is open is:
The ratio of potential difference across AB in the circuit
Describe briefly the Geiger-Marsden scattering experiment. Depict the graph showing the variation of the number of scattered particles detected with the scattering angle. How did this graph lead to the discovery of the nucleus?
A ray of light is incident at an angle \( i \) on a parallel sided glass slab of thickness \( d \) and gets refracted into the slab at angle \( r \). Draw a ray diagram to show its path as it emerges out of the slab. Hence, obtain an expression for the lateral shift of the ray. Under what condition will the shift be minimum?
A conductor of length l and area of cross-section A is connected across an ideal battery of emf V . Derive the formula for the current density in terms of relaxation time τ
Define the term 'drift velocity' of conduction electrons in a conductor.
A ray of light is incident on face AB of a prism ABC with angle of prism \( A \) and emerges out from face AC. The prism is set in the position of minimum deviation with angle of deviation \( \delta \). Find: \begin{enumerate} \item the angle of incidence and \item the angle of refraction on face AB. \end{enumerate}
A laser beam of wavelength 500 nm and power 5 mW strikes normally on a perfectly reflecting surface of area 1 mm\(^2\) of a body. It rebounds back from the surface. Find the force exerted by the laser beam on the body.