List of top Questions asked in CBSE CLASS XII- 2025

Explain the beneficial role of the following, produced as a result of the processes of biotechnology, to mankind:
(α) −1−antitrypsin
What do you mean by activated sludge in an STP?
Explain the biological treatment of the major part of the sludge transferred from the large aeration tank into the anaerobic sludge digesters before its final release into the natural water bodies.
Alien species are highly invasive and are a threat to indigenous species. Substantiate this statement with the help of any two examples.
State any two criteria for determining biodiversity hotspots
If the birds have 18 pairs of autosomal chromosomes and a pair of sex chromosomes, fill in the blanks (i), (ii), (iii) and (iv) in the table given below. (Use symbols Z and W for sex chromosomes).
18 pairs of autosomal chromosomes
Many children in the metro cities are suffering from a very common exaggerated response of the immune system to certain weak antigens in the air. (i) What is the term used for the above mentioned disease?
Name the main type of antibody produced by the immune system in response to this disease.
Which two main inflammation-causing chemicals are produced by the mast cells in such an immune response?
Assertion (A): In some species of asteraceae and grasses, seeds are formed without fertilization.
Reason (R): Formation of fruit without fertilization is called parthenocarpy.
Expand PID. Name any two common viral infections transmitted through sexual contact in human females.
Arrange the given important steps of decomposition in their correct order of occurrence in the breakdown of complex organic matter and explain the fourth step in the process.
\( \fbox{Catabolism}\) \(\fbox{Leaching} \fbox{Fragmentation} \fbox{Mineralisation} \fbox{Humification}\)
The animals that evolved into the first amphibians during evolutionary history were:
Bacteria growing anaerobically on cellulosic material produce large amounts of which gases? Select the correct option.
Assertion (A): In humans, filariasis is characterized by inflammation of the lower limbs.
Reason (R): Filarial worm usually lives in the lymphatic vessels of the lower limbs.
Assertion (A): Isolated single cells can be fused to produce somatic hybrids.
Reason (R): Cells selected for somatic hybridisation have desirable characters.
Some of the important goals of HGP are given below. Choose the correct goal of HGP.
Inheritance of which of the following traits is shown in the cross given below?

Autosomal recessive trait

Choose the correct option from the following:
Given below are few statements with reference to the human male reproductive system:
1. Paired seminal vesicles, prostate gland and bulbourethral gland constitute the male accessory glands.
2. Secretions of the male accessory glands constitute the seminal plasma.
3. Secretions of the bulbourethral glands help in the lubrication of the penis.
4. Enlarged end of the the penis is known as foreskin.
5. Seminal plasma is rich in fructose, calcium and certain enzymes.
Choose the option with all true statements from the given options:
In a DNA, the percentage of thymine is 20. What is the percentage of guanine in it?
Select the statements that are true for the embryo of the flowering plants from the given options:
1. The zygote forms a proembryo and subsequently heart-shaped, globular and mature embryo.
2. Most zygotes divide to form embryo only after a certain amount of endosperm is formed.
3. The embryo develops at the micropylar end of the embryo sac.
4. A typical dicotyledonous embryo consists of an embryonal axis and a scutellum.
Choose the correct option from the following:
Human Immunodeficiency Virus is a member of the group of viruses known as:
When a pure tall pea plant (\textit{Pisum sativum}) with green pod is crossed with a dwarf pea plant with yellow pod, how many dwarf pea plants, out of 16, will be produced in the F\textsubscript{2 generation?}

Derry in On the Face of it is a victim of self-pity. Analyse Derry’s behaviour in the light of the above statement.
 

Select the correct option from those given in brackets, to fill in the blank: The incident made the speaker realize that the discrimination was ____ (dehumanizing / elevating).