List of top Questions asked in CBSE CLASS XII

Restriction Endonuclease – Hind II always cuts DNA molecules at a particular point by recognising a specific sequence of:
The improved trait found in the genetically modified transgenic crop – Golden rice is:
The periodic abstinence by a couple for family planning should be from:
You know that there are twenty different types of naturally occurring amino acids and four different types of bases in the DNA. A combination of 3 such bases codes for a specific amino acid. If instead there are 96 different amino acids and 12 different bases in the DNA, then the minimum number of combination of bases required to form a codon is:
In which of the following plants are both male and female flowers born on the same plant, and the mode of pollination can be geitonogamy or xenogamy?
Which one of the following hormones is secreted by the human placenta that helps in the maintenance of pregnancy?
You are Shiksha/Sameer of XI-C. Write an article for your school magazine on the benefits of participating in the co-curricular activities of the school. Use the given cues along with your own ideas to compose this article.
You are Shiksha/Sameer of XI-C. Write an article for your school magazine
A book fair was organized in your city, Birnagar. Thousands of people including a large number of students visited and benefitted from the fair. It aroused a great interest in the revival of buying and reading books. You want that such book fairs should be organized in other cities of the state to promote the habit of reading. Write a letter to the editor of a national daily sharing your views on the issue and suggesting ways of encouraging reading as a habit. You are Vinod/Vanita of F-115, Roop Nagar, Birnagar.
A book fair was organized in your city, Birnagar
Determine the number of units (\( x \)) that should be sold to maximise the revenue \( R(x) = x \cdot p(x) \). Also verify the result.
(a) Define current density. Scalar or vector? E field in a conductor (n electrons/volume, mass m, charge -e, relaxation time τ). Show j = αE, where α = ne²/mτ. (b) What's a Wheatstone bridge? Balance conditions?
(i) Draw a step-up transformer diagram. Describe its working principle. Explain 3 energy loss causes.
(ii) Does a step-up transformer violate energy conservation? Explain.
(iii) A step-up transformer (N_p=200, N_s=3000) has V_p=90V, I_s=2A. Calculate V_s and I_p.
A ray of light is incident normally on a refracting face of a prism of prism angle A and suffers a deviation of angle δ. Prove that the refractive index n of the material of the prism is given by:n = sin(A+δ)/sin A
The refractive index of the material of a prism is √2. If the refracting angle of the prism is 60◦, find:
(1) Angle of minimum deviation:
(2) Angle of incidence:
Define coherent sources. Can two independent sodium lamps be coherent?
A beam of light consisting of a known wavelength 520 nm and an unknown wavelength λ, used in Young’s double-slit experiment, produces two interference patterns such that the fourth bright fringe of unknown wavelength coincides with the fifth bright fringe of known wavelength. Find the value of λ.
(a) "EM wavelength correlates with the size of the radiating system." Give two examples.
(i) Why do long-distance radio broadcasts use shortwave bands?
(ii) Why are X-ray telescopes satellite-based, while optical/radio telescopes are ground-based?
(i) Derive the impedance of an R-C series circuit connected to an AC source v = v_m sin(ωt).
(ii) When does an inductor act as a conductor? Explain.
(iii) A lamp (R) and inductor (L) in series with 220V-50Hz AC give 11A. With 110V DC, it gives 11A. Find L.
Coils P and Q. Current in P induces current in Q. (a) Explain the phenomenon. (b) Two factors affecting current in Q. (c) Direction of current in Q when current is in P and (i) R increases, (ii) R decreases.
(a) Two characteristic properties of nuclear force. (b) Plot potential energy of a nucleon pair vs. separation. Two conclusions from the plot.
A transformer has 500 primary turns and 5000 secondary turns. Input is 220V-50Hz. What's the output?
Who first produced and observed EM waves in the 25mm-5mm range?
Differentiate between diffusion and drift current. Explain their role in p-n junction formation.
An air-filled parallel plate capacitor (d = 1mm, C = 20pF) is charged to 4.0µC. Find work done to increase plate separation to 5mm (constant charge).
(a) State Bohr's postulates for the hydrogen atom.
(b) A hydrogen atom de-excites from level n to (n-1). Show that emitted frequency ν ∝ α/n³ for large n (α = constant).
Two batteries (6V, 0.8Ω and 3V, 0.2Ω) are connected in series with external resistance R. Find R so that the potential difference across the 6V battery is zero.