Ans: CnH2n+2 is the general formula for the alkane series. So, the second member of the alkane family is ethane
Q.2. what is the magnification of the images formed by plane mirrors and why?
Ans: The magnification of the image formed by a plane mirror is 1. This is because the size of the image formed is equal to the height of the object
Q.3. What is meant by power of a lens?
Ans: The power of a lens the ability of the lens to converge or diverge an incident beam focused on it. P = 1/f
Q.4. Write two differences between binary fission and multiple fission in a tabular form.
Only two daughter cells are produced.
Nuclear division is immediately followed by cytoplasmic division.
More than two daughter cells are produced.
Nuclear division is not immediately followed
Q.5. (a) Why do we need to manage our resources carefully? (b) Why management of natural resources requires a long term perspective?
(a) Since natural resources are limited and its demand is increasing day to day due to growth population
(b) The management of natural resources requires a long-term perspective so that these will last for the future generations
Q6. List four measures that can be taken to conserve forests.
Ans: four measures that can be taken to conserve forests are:
1) Indiscriminate deforestation should be prohibited. 2) Wastage of timber and fuel wood to be avoided.
3) Alternative sources of energy, such as biogas should be used to supplement fuel wood.
4) Forest fires should be prevented.
Q.7. Na, Mg and Al are the elements of the same period of Modern Periodic Table having, one, two and threevalance electrons res. Which of these elements
(i) has the largest atomic radius, (ii) is least reactive? Justify your answer stating reason Solution:
Ans: (i) sodium has the largest atomic radius. On going from left to right in the periodic table, atomic radius decreases due to increase in nuclear pull due to addition of proton.
(ii) Aluminum is the least reactive element. On going from left to right in the periodic table, the reactivity decreases due to increased nuclear charge require more energy to lose electron.
Q.8. From the following elements: 4Be; 9F; 19K; 20Ca
(i) Select the element having one electron in the outermost shell. (ii) Two elements of the same group.
Write the formula of and mention the nature of the compound formed by the union of 19K and element x ( 2 , 8, 7)
Ans: Electronic configuration of 4Be -------- 2, 2.
Electronic configuration of 9F is --------- 2, 7
Electronic configuration of 19 K is --------- 2, 8, 8, 1
Electronic configuration of 20Ca is ------------ 2, 8, 8, 2.
(i) K (ii) Be and Ca
Electronic configuration of element X is 2, 8, 7.
Valency of X = 8 − 7 = 1 and Valency of K = 1
Therefore, the formula of the compound formed when K and element X combine is KX. The compound KX is ionic compound
Q.9. What is meant by isomers? Draw the structures of two isomers of butane, C4H10. Explain why we cannot have isomers first three of alkane series.
Ans: Isomers are the compounds that have the same molecular formula but different structural formulae.
Following are the isomers of butane: CH3CH2CH2CH3 butane
Q.10. What is the difference between the molecules of soaps and detergents, chemically? Explain the cleansing action of soap?
Soaps are sodium salt of long chain carboxylic acid where as detergents are the Ammonium or sulphate of long chain of carboxylic acid.
When dirty clothes are mixed with water and soap, the ionic part of the soap being water attractive, dissolves in water whereas the hydrocarbon part of the soap being water repellent unites with the oil or greese part. When dirty clothes are rinsed with water, the dirt particles attached with the soap molecules, dissolve in water and come out. In this way, clothes become clean.
Q.11. what are sexually transmitted diseases. List two example of each diseases caused due to (i) bacterial infection and (ii) viral infections. Which device or devices may be used to prevent the spread of such diseases?
Diseases that are transmitted from one person to other through sexual contact are known as sexually transmitted
Examples of STDs caused by bacterial infection: Gonorrhoea and Syphilis
Examples of STDs caused by viral infection: Herpes and Acquired immunodeficiency syndrome (AIDS)
Use of condoms can prevent the spread of these diseases to a great extent
Q.12. What is DNA copying? State its importance.
Ans: DNA Copying is the process of production of a new DNA molecule from an already existing DNA molecule through chemical reaction. It is accompanied with the creation of new cellular apparatus so that the daughter DNA and parent DNA Importance of DNA copying
1. Copying helps in the transmission of characteristics from parents to offspring.
2. Copying ensure that when cell multiplies, through the mechanisms of mitosis and meiosis, the equal amount of DNA (genetic material) passes in to the new cell.
Q.13. Explain budding in hydra with the help of labeled diagrams only.
Ans: Budding involves the formation of a new individual from a protrusion called the bud. In Hydra, the cells divide rapidly at a specific site and develop as an outgrowth called a bud. These buds, while attached to the parent plant, develop into small individuals. When this individual becomes large enough, it detaches itself from the parent body to exist as an independent individual
Ans: The formation of a new species by evolution or any genetic modification of the previously existing species is called speciation
Following are the factors responsible for speciation: 1. Genetic drift 2. Natural selection 3. Reproductive isolation 4. Geographical isolation
Q.15. (i) Planaria, insects, octopus and vertebrates all have eyes. Can we group eyes of these animals together to establish evolutionary origin? Justify your answer.
(ii) "Birds have evolved from reptiles" State evidence to prove the statement.
Ans: (i) The eyes seen in Planaria, insects, octopus and vertebrates vary greatly in their structure. These organisms can be used for studying evolution of eyes as the eye of Planaria is simple without lens, insects have compound eyes and vertebrates have highly specialized eye however, all of them perform same function, that is, vision. Thus, a common evolutionary origin can be established
(ii) Birds have evolved from reptiles as the connecting link between reptiles and birds is Archaeopteryx, Also there are some similarities in birds and reptiles. Birds have four-chambered heart, which is also a feature of some reptiles. they have separate sexes and internal fertilization occurs in both birds and reptiles.