T2.m2.C10 science


CBSE 10th Term-2 2022 : Science Important 2 Marks Questions with Solution

Chapter – 4

Carbon and its Compounds

Que 1. The element carbon forms a very large number of compounds. Give reason for this fact.

Ans 1. Carbon is the only element that can form so many different compounds because each carbon atom can form four chemical bonds to other atoms, and because the carbon atom is just the right, small size to fit in comfortably as parts of very large molecules.

Que 2. Covalent compounds generally don't conduct electricity. Why?

Ans 2. A covalent bond is formed between non-metal atoms which combine together by sharing electrons. Covalent compounds have no free electrons and no ions so they dont conduct electricity

Que 3. State two characteristic features of carbon which when put together give rise to a large number of carbon compounds.

Ans 3. (i) The size of carbon atom is very small (Atomic radius = 77pm)
(ii) The strength C-C bond is quite high (355 kJ mol−1)
therefore, any number of carbon atoms can be linked by covalent bonds. This self linking property is called catenation.

Que 4. What is catenation?

Ans 4. Catenation : It is the phenomenon of an atom to form a strong covalent bond with the atoms of itself. Carbon shares the property of catenation to maximum extent because it is small in size and can form  -  multiple bonds to itself. The following conditions are necessary for catenation,

(i) the valency of element is greater than or equal to two.

(ii) Element should have an ability to bond with itself.

(iii) The self bond must be as strong as its bond with other moleculas.

(iv) Kinetic inertness of catenated compound towards other molecules.

Carbon possesses all the above properties and forms a wide range of compounds with itself.

Que 5. What do you mean by tetravalency of carbon?

Ans 5. Carbon atom has 4 electrons in valence shell. So it will complete its octet by sharing its four valence electrons with other atoms. Carbon forms four covalent bonds by sharing valence electrons. This is called as tetravalency of carbon.

Que 6. Define structural isomerism. Draw the structures of two isomers of butane.

Ans 6. Isomers are compounds having the same molecular formula but different structures.

The two isomers of butane, C4HI0 are:

Since branching is not possible, isomers are not possible for the first three members of alkane series.

Chapter – 5

Periodic Classification of Elements

Que 1. How does the tendency to lose electrons change in a group and why?

Ans 1. The tendency to lose electrons increases when we move from top to bottom in a group. This is because the atomic size of the atoms increases doesn't the group and the valence shell electrons increases due to which the nuclear power which the electron closer to the nucleus decreases. On the other hand, when we move from left to right in a period the tendency of the atom to lose electron decreases be use the atomic size decreases along the period and the valence shell electrons also decreases due to which nucleus exert stronger force on the valence shell electrons.

Que 2. Why He, Ne, and Ar are called inert gases?

Ans 2. He Ne and Ar are called inert gases because their outermost shell is complete and they do not lose or gain electrons in their outermost shell hence they have zero valency.

Que 3. Write two limitations of Mendeleev's Periodic Table.

Ans 3. Two limitations of Mendeleev's Periodic Table are :

(i) The position of isotopes could not be explained.
(ii) No fixed position for hydrogen

Que 4. Why is the position assigned to hydrogen in the periodic table considered anomalous?

Ans 4. Hydrogen resembles both alkali metals and halogens. It can lose one electron like alkali metals and also gain one electron like halogens. Therefore, position assigned to hydrogen in the periodic table is considered anomalous.

Que 5. How does the metallic character of an element vary as we go down a group? Give reason for this variation.

Ans 5. Metallic character decreases as you move across a period in the periodic table from left to right. This occurs as atoms more readily accept electrons to fill a valence shell than lose them to remove the unfilled shell. Metallic character increases as you move down an element group in the periodic table.

Que 6. Why metallic oxides are basic in nature whereas non-metallic oxides are acidic in nature?

Ans 6. Metallic oxides are basic in nature because they react with dilute acids to form salt and water. They also react with water to form metal hydroxides which are alkaline in nature because these metal hydroxides release OH- ions in solution. ... Therefore, non metallic oxides would be acidic in nature.

Que 7. How does the atomic size vary as we go down a group?

Ans 7. Atomic size increases as we go down a group because each time one new shell is added and electrons in the outermost shell move away from the nucleus.

Que 8. Four elements P, Q, R and S have atomic number 12, 13, 14 and 15 respectively. Answer the following:

(a) Classify these elements as metals and non-metals.

Ans (a). (ii) Elements P and Q are metals as they have 2 electrons in their valence shell and they are positively charged ions whereas elements R and S are non-metals as they gain electrons to complete their octet.

(b) Which of these elements will form the most basic oxide?

Ans (b). P and Q will form basic oxides as they are metals.

Que 9. (a) How do we calculate the valency of an element from its electronic configuration?

Ans 9 (a). The valency of an element is determined by the number of valence electrons present in the outermost shell of the atom.
For elements of group 1, 2, 13 and 14, the valency is equal to the number of valence electrons and for elements of group 15, 16, 17 and 18, the valency is equal to 8 minus number of valence electrons.

(b) How does valency of an element vary across a period?

Ans 9 (b). The valency of an element is dependent on the number of electrons in the outermost shell of the electron. In a group all constituting elements will have the same valency because they all have the same number of electrons in the outer shells. Across the a period, the number however increase by 1.

Que 10. How many groups and periods are present in the Modern Periodic Table?

Ans 10. Modern Periodic Table has 18 groups and 7 periods.

Chapter – 8

How Do Organisms Reproduce?

Que 1. Write two important functions of testosterone.

Ans 1. Testis is a male gonad and is located in the scrotum, outside the body. Testosterone is the male hormone which is secreted from the interstitial cells of testis.

The functions of testosterone are :

  • It helps in the growth of testis in puberty.
  • It also helps in the growth of secondary sex organs in male like scrotum, prostate gland etc. in puberty.

Que 2. What is placenta? Also write its functions.

Ans 2. Placenta - A special tissue embedded in the uterus wall with the help of which human embryo gets nutrition from mother’s blood.

(i) To provide large surface area for glucose and oxygen to pass through mother’s blood to the embryo.

(ii) The metabolic waste generated by embryo is removed through placenta into mother’s blood.

Que 3. Why do we see different types of organisms around us?

Ans 3. The different variety of living organisms around us represents biodiversity.

Biodiversity may be the result of the

1) variation at genetic and species level etc.
2) different types of habitats.
3) difference in conditions of ecosystems etc.

Que 4. What is the importance of variation?

Ans 4. It helps a species to survive,it also helps us to determine who is who,it helps organisms to adapt to their environment as well as to changes which do occur in the environment,however it also helps a species to emerge strong if favoured by natural selection. variation helps a species to be resistant to diseases, thus if a species is to survive there has to be variation.

Que 5. Why is vegetative propagation practiced for growing some types of plants?

Ans 5. Vegetative propagation is practiced because:

i. It is more rapid and easier method.

ii. It can help plant to grow in regions where germination failed.

iii. It is useful for propagating those plants that do not produce viable seeds or  produce less number of seeds.

iv.. it is quick method of producing several plants in short period of time.

Que 6. Write names of male and female sex hormones.

Ans 6. Male sex hormone is testosterone and female sex hormone is osterogen. These are responsible for secondary sexual characters.

Que 7. Mention the parts of a flower.

Ans 7. There are four main parts of a flower and they are :

(i) Sepals: Green-colored part that covers the flower in its initial stage.

(ii) Petals: These form the colored part of the plant.

(iii) Stamen: It bears anther and filament.

(iv) Pistil: This is the innermost part of a flower. It bears stigma, style, and ovary.

Que 8. What is the effect of DNA copying which is not perfectly accurate on the reproduction process?

Ans 8. The DNA copying which is not perfectly accurate in the reproduction process results in variations in populations for the survival of species.If the variation are more drastic then the DNA will not be able to function properly leading to the death of the cell.

Chapter – 9

Heredity and Evolution

Que 1. Explain sex determination.

Ans 1. i. The mechanism of determining the sex of an individual is known a sex determination.

ii. In some organisms, environmental factors such as temperature determine the sex of the organism in the egg.

iii. Each human cell contains 23 pairs (46 numbers) of chromosomes, out of which 22 pairs are called autosomes, which are similar in both males and females and are responsible for the various characteristics of an individual. The last pair is that of the sex chromosomes that determine the sex of the individual. Sex chromosomes in humans are of two types X and Y.

iv. Females have two X chromosomes in their cells while males have one X and one Y in their cells.

v. When the sperm containing the X chromosome fertilises the egg, then the zygote develops into a female. When the sperm containing the Y chromosome fertilises the egg, then the zygote develops into a male.

Que 2. What are genes? Where are they located?

Ans 2. The basic functional unit of heredity are called genes. They are also the structural unit of heredity. They are located on chromosomes and their locations are called loci (singular-locus). Genes could be the sequence of DNA in some organisms and those of RNA in some others. Transcriptionally active genes usually code for proteins that have specific functions.

Que 3. What is meant by dominant genes and recessive genes? Give one example of each.

Ans 3. The gene which decides the appearance of an organism even in the presence of an alternative gene is known as dominant gene. The gene which can decide the appearance of an organism only in the presence of another identical gene is called a recessive gene. For example, in pea plants, the dominant gene for tallness is T and the recessive gene for dwarfism is t.

Que 4. What are sex chromosomes?

Ans 4. Sex chromosomes are those chromosomes that determine the sex of an individual. For example, in humans, two sex chromosomes, X and Y are present. Individuals with XX combination are females, while those with XY combination are males.

Que 5. Distinguish between autosomes and sex chromosomes.

Ans 5. 

 AutosomesSex chromosomes
  • Autosomes control the somatic characters of the body.
  • Example: eye colour, height, etc.
  • Out of 23 pairs 22 pairs of chromosomes are autosomes.
  • Sex chromosomes determine sex of the organism and they govern the sex linked traits of an organism.
  • Example: baldness, colour blindness.
  • Out of 23 pairs one pair is of sex chromosomes. XX in females and XY in males.

Que 6. Name the four blood groups in human.

Ans 6. O , A, B, AB these are the four blood groups in human beings.

Que 7. Why did Mendel choose pea plants for conducting his experiments on inheritance?

Ans 7. Mendel chose pea plants for studying inheritance because of the following reasons:

  • Pea plants had a number of clear cut differences which were easy to tell apart. For example, some pea plants were 'tall' whereas others were 'dwarf'.
  • They were self pollinating plants.
  • Many generations of pea plants can be produced in a comparatively short time span and their study is much simpler than that of animals.

Que 8. What does law of segregation states?

Ans 8. The law of segregation states that the two alleles of a single trait will separate randomly, meaning that there is a 50% either allele will end up in either gamete. This has to do with 1 gene.

Que 9. Write down the phenotypic ratio and genotypic ratio in monohybrid cross.

Ans 9. A cross between two types of plants of same species considering only the transmission of one character is called monohybrid cross.

Genotypic Ratio - 1:2:1

Phenotypic Ratio - 3:1

Chapter – 12


Que 1. What is electrical resistivity of a material? Write its unit.

Ans 1. The electrical resistivity of a material is defined as the resistance offered to current flow by a conductor of unit length having unit area of cross section. The unit of ρ is ohm−m(Ωm)

Que 2. What is the commercial unit of electric energy? Convert it into joules.

Ans 2.  The commercial unit of energy is  kilo-Watt-hour (kWh)

it is used in daily life because SI unit 'joule' is too small to express very large quantities of energy.

1 kWh in joule :

1kWh = 1kW × 1h

=1000W × 1h

=1000Js-1 × 3600s

 1kWh = 3600000J

1kWh = 3.6 × 106J

1 kWh in joule can be expressed as 3.6 × 106J

Que 3. State Ohm’s law. Write the necessary conditions for its validity.

Ans 3. Ohm’s law : When the physical conditions such as temperature etc. remain same, the current flowing through the conductor is directly proportional to the potential difference applied across the ends of the conductor, i.e.,

I ∝ V or V ∝ I

⇒ V = IR

Que 4. Define electric power. Express it in terms of potential difference V and resistance R.

Ans 4. Electric power: It is the rate of doing work by an energy source or the rate at which the electrical energy is dissipated or consumed per unit time in the electric circuit is called electric power.

So, Power P = Work done (w)/Time (t)

= Electrical energy dissipated/Time (t)

= Vl = V2/R

Que 5. An electrical fuse is rated at 2 A. What is meant by this statement?

Ans 5. It means: the maximum current will flow through it is only 2 A. Fuse wire will melt if the current exceeds 2 A value through it.

Que 6. State difference between the wire used in the element of an electric heater and in a fuse wire.

Ans 6. The wire used in the element of electric heater has a high resistivity and have a high melting point, i.e. even at a high temperature element do not burn while fuse wire have a low melting point and high resistivity.

Chapter – 13

Magnetic effects of current

Que 1. What is meant by solenoid?

Ans 1. Solenoid: A coil of many circular turns of insulated copper wire wound on a cylindrical insulating body (i.e., cardboard etc.) such that its length is greater than its diameter is called solenoid.

Que 2. What is an electromagnet? What is the direction of magnetic field lines?

Ans 2. 

Que 3. What is the shape of magnetic field lines due to a straight current carrying conductor?

Ans 3. The Magnetic field lines around a straight conductor carrying current are concentric circles whose centres lie on the wire. The direction of magnetic field lines can be determined using Right-Hand Thumb Rule.

Que 4. Why do magnetic field lines not intersect each other?

Ans 4. If magnetic field lines intersect each other, then at the intersection point there will be two directions of the same field which is not possible. Hence the field lines do not cross or intersect each other.

Que 5. How is the strength of magnetic field near a straight current carrying conductor related to the strength of current in the conductor?

Ans 5.

  • Conductors are the materials or substances which allow electricity to flow through them.
  • They conduct electricity because they allow electrons to flow easily inside them from atom to atom.
  • The strength of magnetic field around a straight current conductor increases on increasing the strength of current in the conductor or vice versa. 

Que 6. Write one application of each of the following:
(a) Right-hand thumb rule
(b) Flemings left hand rule
(c) Flemings right hand rule

Ans 6. (a) Right-hand thumb rule is used to find the direction of magnetic field due to straight current carrying conductor. According to this, if the thumb points in the direction of current then the curl of fingers gives us the direction of magnetic field.

(b) Fleming’s left hand rule is used to find the direction of force exerted on a current-carrying conductor placed in a magnetic field as in electric motor. According to this, if you hold your thumb, index finger and middle finger at right angles to each other, then if index finger points in the direction of the magnetic field and middle finger points in the direction of current, then thumb gives us the direction of force.

(c) Fleming’s right hand rule is used to find the direction of induced current in a closed circuit placed in changing magnetic field as in electric generator. According to this, if you hold your thumb, index finger and middle finger at right angles to each other, then if thumb is along the direction of motion of conductor and index finger points in the direction of magnetic field, then middle finger points in the direction of induced current.

Que 7. List two properties of magnetic field lines.

Ans 7. Properties of magnetic field is:

  • They seek the path of least resistance between opposite magnetic poles.
  • They never cross one another.
  • They all have the same strength.

Que 8. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?

Ans 8. The force experienced by a current carrying conductor is largest when the directions of magnetic field and electric current are perpendicular to each other.

Chapter – 15

Our Environment

Que 1. Explain how does making of Kulhads affect our environment?

Ans 1. Kulhads are made of soil. Use of earthen kulhads is not an environmentally friendly decision because for making enough kulhads upper layer of fertile soil is used. Loss of fertile soil can make the land barren and unproductive that is, unfit for any agricultural activity.

Que 2. State two differences between a consumer and producer.

Ans 2.The differences between the producers and consumers are as follows:

DefineProducers are those organisms, who have an ability to produce food for themselves.Consumers are those organisms which depend upon other organisms for food.
Level in the food chainProducers forms the base of the food chain pyramid.Consumers are the top most organisms in the food chain pyramid.
Energy utilizationFrom sunFrom producers
ExamplesPlantsHerbivores or carnivorous.

Que 3. Draw the line diagram showing flow of energy in an ecosystem.

Ans 3.

Que 4. Define a food web. State its significance for ecosystem.

Ans 4. A network of interconnecting food chains in a natural community of different organisms is called a food web.

Significance of food web:

(1) Food webs permit alternative foods.

(2) They ensure a better chance of survival of an organism, in case any of its food source happens to be scarce.

Que 5. What are phytoplanktons?

Ans 5. Phytoplankton is the base of several aquatic food webs. In a balanced ecosystem, they provide food for a wide range of sea creatures.Phytoplankton also require inorganic nutrients such as nitrates, phosphates, and sulfur which they convert into proteins, fats, and carbohydrates.

Que 6. What will happen if all the phytoplanktons are eliminated from pond?

Ans 6. Phytoplanktons are very small members of plant kingdom. Phytoplanktons make food for pond ecosystem and functioning as producer. Zooplankton and small animals and fishes use phytoplanktons as food and these animals eat by higher fishes and complete the food chain . As we can see if phytoplanktons are not there nobody can survive.

Que 7. What is an ecosystem? List its two main components.

Ans 7. Ecosystem is a self sustaining system where the biotic and abiotic organisms of various communities interact with each other.

(I) The two components of the ecosystem are - Biotic and Abiotic. 

(II) Ponds are the example of natural ecosystem whereas the aquarium is an example of artificial ecosystem.

Que 8. Name two natural ecosystems.

Ans 8. There are two main types of natural ecosystems:

  • Terrestrial ecosystem: Land-based.
  • Aquatic ecosystem: Water-based.

Que 9. We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly. Explain.

Ans 9. Ponds and lakes are natural ecosystems and they contain decomposers. Decomposers act as cleansing agents here, whereas an aquarium is an artificial ecosystem, it does not contain decomposers that cleanse it. Therefore the aquarium needs to be cleaned regularly.