CBSE

Hydrogen  1. Justify the position of hydrogen in the periodic table on the basis of its electronic configuration. 2. Write the names of isotopes of hydrogen. What is the mass ratio of these isotopes? 3. Why does hydrogen occur in a diatomic form rather than in a monoatomic form under normal conditions? 4. How can … Read more

Miscellaneous Exercise 1. Write the negation of the following statements: (i) For every positive real number , the number is also positive. (ii) All cats scratch. (iii) For every real number , either or (iv) There exists a number such that Ans. (i) There exists a positive real number such that is not positive. (ii) … Read more

16. Why does the following reaction occur? What conclusion about the compound (of which is a part) can be drawn from the reaction. 17. Consider the reactions: (a) (b) (c) (d) What inference do you draw about the behaviour of and from these reactions? 18. Balance the following redox reactions by ion-electron method: (a) (in … Read more

17. Compare the structures of . 18. What do you understand by the term ‘auto-protolysis’ of water? What is its significance? 19. Consider the reaction of water with and suggest, in terms of oxidation and reduction, which species are oxidized/reduced. 20. Complete the following chemical reactions. (i) (ii) (iii) (iv) (v) Classify the above into … Read more

Exercise 15.1 Find the mean deviation about the mean for the data in Exercises 1 and 2. 1. 4, 7, 8, 9, 10, 12, 13, 17 Ans. Mean of the given data Mean deviation about mean = = = 3 2. 38, 70, 48, 40, 42, 55, 63, 46, 54, 44 Ans. Mean of the … Read more

The s block elements  1. What are the common physical and chemical features of alkali metals? 2. Discuss the general characteristics and gradation in properties of alkaline earth metals. 3. Why are alkali metals not found in nature? 4. Find the oxidation state of sodium in 5. Explain why is sodium less reactive than potassium? … Read more

Exercise 15.2 Find the mean and variance for each of the data in Exercises 1 to 5. 1. 6, 7, 10, 12, 13, 4, 8, 12 Ans. Given: = 6, 7, 10, 12, 13, 4, 8, 12 = 6 + 7 + 10 + 12 + 13 + 4 + 8 + 12 = 72 … Read more

16. Starting with sodium chloride how would you proceed to prepare (i) sodium metal (ii) sodium hydroxide (iii) sodium peroxide (iv) sodium carbonate? 17. What happens when (i) magnesium is burnt in air (ii) quick lime is heated with silica (iii) chlorine reacts with slaked lime (iv) calcium nitrate is heated ? 18. Describe two … Read more

Exercise 15.3 1. From the data given below state which group is more variable, A or B: Ans. Group A Mean = = 45 – 0.4 = 44.6 Standard deviation = = = = 15.09 Group B Mean = = 45 – 0.4 = 44.6 Standard deviation = = = = 15.61 2. From the … Read more

20. What happens when (a) Borax is heated strongly, (b) Boric acid is added to water, (c) Aluminium is treated with dilute NaOH, (d) is reacted with ammonia? 21. Explain the following reactions (a) Silicon is heated with methyl chloride at high temperature in the presence of copper; (b) Silicon dioxide is treated with hydrogen … Read more

Exercise 12.1 1. A point is on the axis. What are its coordinates and coordinates? Ans. We know that coordinates of any point on the axis will be Therefore, coordinate and coordinate of the point are zero. 2. A point is on XZ-plane. What can you say about its coordinate? Ans. We know that coordinates … Read more

Miscellaneous Exercise 1. The mean and variance of eight observations are 9 and 9.25 respectively. If six of the observations are 6, 7, 10, 12, 12 and 13, find the remaining two observations. Ans. Let two required observations be and Then, According to question, ……….(i) Also ……….(ii) When then on solving and we get and … Read more