List of top Questions asked in CBSE CLASS XII

How is the rate of decomposition affected by the nature of detritus and temperature?
Write the role of ’ori’ and restriction site in the cloning vector pBR322.
Although Hemophilia and sickle cell anemia are two blood-related Mendelian disorders, yet they differ in their pattern of inheritance. State any two differences.
(a) Name any two copper releasing intra-uterine devices. State two reasons that make them effective contraceptives.
(b) Name any two outbreeding devices that flowering plants have developed and explain how they help in encouraging cross-pollination.
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): 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.
Assertion (A): Virus-infected cells produce interferons.
Reason (R): Interferons can cause inflammation of virus-infected cells.
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.
The pyramid of biomass in the sea is generally inverted because in the sea:
Which one of the following is not a feature of plasmids?
Which one of the following pairs is not correctly matched?
The vector for dengue fever is:
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:
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:
Which one of the following statements is not true?
In humans, the secondary oocyte completes meiotic division when:
Match the items in Column I with those in Column II and select the correctly matched option from those given below: 
Cross Phenotypic Ratio
An angiosperm embryo sac is located within the:
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 briefly diffraction of light from a single slit and draw the shape of the diffraction pattern.
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.
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.
Discuss four main causes of energy loss in a real transformer.