Q. 1. Write the name and formula of the 2nd member of homologous series having general formula CnH2n
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