List of top Questions asked in CBSE CLASS XII

Assertion (A): Loss of biodiversity can occur due to overexploitation of resources.
Reason (R): Introduction of Clarias gariepinus in Indian rivers has led to a decline in native Indian fishes.
Assertion (A): Virus-infected cells produce interferons.
Reason (R): Interferons can cause inflammation of virus-infected cells.
The pyramid of biomass in the sea is generally inverted because in the sea:
Assertion (A): RNA is unstable and can mutate at a faster rate.
Reason (R): The presence of 2’-OH group in every nucleotide of RNA makes it labile and easily degradable.
Assertion (A): Specific enzymes are used to degrade the cell wall in organisms to isolate the DNA from the cell.
Reason (R): Fungal cell wall is degraded by the enzyme cellulase.
Which one of the following pairs is not correctly matched?
A woman with normal vision has a colour blind father. She marries a man with normal vision. The percentage chance of their progeny being colour blind is:
The vector for dengue fever is:
Which one of the following is not a feature of plasmids?
In a ’transcription unit’, the ’terminator’ is located towards the:
In the double helical structure of DNA molecule, the strands are:
A population is in genetic equilibrium/Hardy-Weinberg equilibrium for a gene with 2 alleles (dominant allele is ‘A’ and recessive allele ‘a’). If the frequency of allele ‘A’ is 0.6, then the frequency of genotype ‘Aa’ is:
In humans, the secondary oocyte completes meiotic division when:
Which one of the following statements is not true?
An angiosperm embryo sac is located within the:
Which of the following is a polar molecule?
In a diode, the reverse current is practically not dependent on the applied voltage.
A thin spherical shell of radius \( R \) has a uniform surface charge density \( \rho \). Using Gauss' law, deduce an expression for the electric field:
(i) Outside the shell.
(ii) Inside the shell.
A plane light wave propagating from a rarer into a denser medium, is incident at an angle \( i \) on the surface separating two media. Using Huygen’s principle, draw the refracted wave and hence verify Snell’s law of refraction.
In a Young’s double slit experiment, the slits are separated by 0.30 mm and the screen is kept 1.5 m away. The wavelength of light used is 600 nm. Calculate the distance between the central bright fringe and the 4thx dark fringe.
In a series LCR circuit, establish the conditions under which:
[(i)] impedance is minimum and
[(ii)] wattless current flows in the circuit.
Discuss briefly diffraction of light from a single slit and draw the shape of the diffraction pattern.
Describe the construction and working of a transformer and hence obtain the relation for \( \frac{V_s}{V_p} \) in terms of the number of turns of primary and secondary.
An object is placed between the pole and the focus of a concave mirror. Using mirror formula, prove mathematically that it produces a virtual and enlarged image.
Discuss four main causes of energy loss in a real transformer.