Which postulate of Dalton’s atomic
[question] Question. Which postulate of Dalton’s atomic theory can explain the law of definite proportions? [question] [solution] Solution: The postulate of Dalton’s atomic theory based on the law of definite proportion is: "The relative number and kind of atoms in a given compound remains constant." [/solution]...
Read More →The following number of goals was scored by a team in a series of 10 matches:
[question] Question. The following number of goals was scored by a team in a series of 10 matches: 2, 3, 4, 5, 0, 1, 3, 3, 4, 3 Find the mean, median and mode of these scores. [/question] [solution] Solution: The number of goals scored by the team is 2, 3, 4, 5, 0, 1, 3, 3, 4, 3 Mean of data $=\frac{\text { Sum of all observations }}{\text { Total number of observations }}$ Mean score $=\frac{2+3+4+5+0+1+3+3+4+3}{10}$ $=\frac{28}{10}=2.8$ $=2.8 \mathrm{goals}$ Arranging the number of goals in as...
Read More →Which postulate of Dalton’s atomic theory is the result of the law
[question] Question. Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass? [/question] [solution] Solution: The postulate of Dalton’s atomic theory is, atoms are indivisible particles, which can neither be created nor destroyed in a chemical reaction. [/solution]...
Read More →What would you observe when zinc is added to a solution of iron
[question] Question. What would you observe when zinc is added to a solution of iron (II) sulphate? Write the chemical reaction that takes place. [/question] [solution] solution: Zinc is more reactive than iron. Therefore, if zinc is added to a solution of iron (II) sulphate, then it would displace iron from the solution and green colour of $\mathrm{FeSO}_{4}$ solution will fade. $\mathrm{Zn}(\mathrm{s})+\mathrm{FeSO}_{4}(\mathrm{aq}) \rightarrow \mathrm{ZnSO}_{4}(\mathrm{aq})+\mathrm{Fe}(\mathr...
Read More →Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water.
[question] Question. Hydrogen and oxygen combine in the ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas? [/question] [solution] Solution: It is given that the ratio of hydrogen and oxygen by mass to form water is $1: 8$. Then, the mass of oxygen gas required to react completely with $1 \mathrm{~g}$ of hydrogen gas is $8 \mathrm{~g}$. Therefore, the mass of oxygen gas required to react completely with $3 \mathrm{~g}$ of hy...
Read More →Which gas is produced when dilute hydrochloric acid is added to a reactive metal?
[question] Question. Which gas is produced when dilute hydrochloric acid is added to a reactive metal? Write the chemical reaction when iron reacts with dilute $\mathrm{H}_{2} \mathrm{SO}_{4}$. [/question] [solution] solution: Hydrogen gas is evolved when dilute hydrochloric acid is added to a reactive metal. When iron reacts with dilute $\mathrm{H}_{2} \mathrm{SO}_{4}$, iron (II) sulphate with the evolution of hydrogen gas is formed. $\mathrm{Fe}(\mathrm{s})+\mathrm{H}_{2} \mathrm{SO}_{4}(\math...
Read More →Use Euclid's division lemma to show that the cube of any positive integer is of the form $9 \mathrm{~m}, 9 \mathrm{~m}$ $+1$ or $9 m+8$.
[question] Question. Use Euclid's division lemma to show that the cube of any positive integer is of the form $9 \mathrm{~m}, 9 \mathrm{~m}$ $+1$ or $9 m+8$. [solution] Solution: Any positive integer is of the form $3 q, 3 q+1,3 q+2$ Case1: Let, $\mathrm{n}=3 \mathrm{q}$ Cube of this will be $n^{3}=27 q^{3}$ $n^{3}=9\left(3 q^{3}\right)$ So, $\mathrm{n}^{3}=9 \mathrm{~m}$, where $\mathrm{m}=3 \mathrm{q}^{3}$ Case2: $\mathrm{n}=3 \mathrm{q}+1$ So, $n^{3}=(3 q+1)^{3}$ $\mathrm{n}^{3}=27 \mathrm{q}...
Read More →Samples of four metals A, B, C and D
[question] Question. Samples of four metals A, B, C and D were taken and added to the following solutions one by one. The results obtained have been tabulated as follows. Use the above table to answer the following questions about metals A, B, C and D. (i) Which is the most reactive metal? (ii) What would you observe if B is added to a solution of copper (II) sulphate ? (iii) Arrange the metals A, B, C and D in the order of decreasing reactivity. [/question] [solution] solution: $\mathrm{A}+\mat...
Read More →In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid.
[question] Question. In a reaction, 5.3 g of sodium carbonate reacted with 6 g of ethanoic acid. The products were 2.2 g of carbon dioxide, 0.9 g water and 8.2 g of sodium ethanoate. Show that these observations are in agreement with the law of conservation of mass. [/question] [solution] Solution: Sodium carbonate reacts with ethanoic acid converted into sodium ethanoate, carbon dioxide,and water $\therefore$ Total mass before the reaction $=$ Total mass after the reaction Hence, the given obse...
Read More →100 surnames were randomly picked up from
[question] Question. 100 surnames were randomly picked up from a local telephone directory and a frequency distribution of the number of letters in the English alphabet in the surnames was found as follows: (i) Draw a histogram to depict the given information. (ii) Write the class interval in which the maximum number of surname lie. [/question] [solution] Solution: (i) Here, it can be observed that the data has class intervals of varying width. The proportion of the number of surnames per 2 lett...
Read More →A random survey of the number of children of various age groups playing in park was found as follows:
[question] Question. A random survey of the number of children of various age groups playing in park was found as follows: Draw a histogram to represent the data above. [/question] [solution] Solution: Here, it can be observed that the data has class intervals of varying width. The proportion of children per 1 year interval can be calculated as follows. Taking the age of children on x-axis and proportion of children per 1 year interval on y-axis, the histogram can be drawn as follows. [/solution...
Read More →The runs scored by two teams A and B on the first 60 balls in a cricket match are given below:
[question] Question. The runs scored by two teams A and B on the first 60 balls in a cricket match are given below: Represent the data of both the teams on the same graph by frequency polygons. [/question] [solution] Solution: It can be observed that the class intervals of the given data are not continuous. There is a gap of 1 in between them. Therefore, $\frac{1}{2}=0.5$ has to be added to the upper class limits and $0.5$ has to be subtracted from the lower class limits. Also, class mark of eac...
Read More →Write equations for the reactions of
[question] Question. Write equations for the reactions of (i) Iron with steam (ii) Calcium and Potassium with water [/question] [solution] solution: [/solution]...
Read More →Use Euclid's division lemma to show that the square of any positive integer is either of the form 3m or 3m + 1 for some integer m.
[question] Question. Use Euclid's division lemma to show that the square of any positive integer is either of the form 3m or 3m + 1 for some integer m. [/question] [solution] Solution: Let a be any odd positive integer. We apply the division lemma with a and $b=3$. Since $0 \leq r<3$, the possible remainders are 0,1 and 2 . That is, a can be $3 \mathrm{q}$, or $3 \mathrm{q}+1$, or $3 \mathrm{q}+2$, where $\mathrm{q}$ is the quotient. Now, $\quad(3 q)^{2}=9 q^{2}$ which can be written in the form...
Read More →Which of the following
[question] Question. Which of the following are chemical changes ? (a) Growth of a plant (b) Rusting of iron (c) Mixing of iron fillings and sand (d) Cooking of food (e) Digestion of food (f) Freezing of water (g) Burning of a candle [/question] [solution] Solution: Rusting of iron, cooking of food, digestion of food, and burning of candle are chemical changes. [/solution]...
Read More →Why sodium is kept immersed
[question] Question. Why sodium is kept immersed in kerosene oil ? [/question] [solution] solution: Sodium and potassium are very reactive metals and combine explosively with air as well as water. Hence, they catch fire if kept in open. Therefore, to prevent accidental fires and accidents, sodium is stored immersed in kerosene oil. [/solution]...
Read More →The following table gives the distribution of students of two sections according to the mark obtained by them:
[question] Question. The following table gives the distribution of students of two sections according to the mark obtained by them: Represent the marks of the students of both the sections on the same graph by two frequency polygons. From the two polygons compare the performance of the two sections. [/question] [solution] Solution: We can find the class marks of the given class intervals by using the following formula. Class mark $=\frac{\text { Upper class limit }+\text { Lower class limit }}{2...
Read More →Explain the meaning of malleable
[question] Question. Explain the meaning of malleable and ductile. [/question] [solution] solution: Malleable: Substances that can be beaten into thin sheets are called malleable. For example, most of the metals are malleable. Ductile: Substances that can be drawn into thin wires are called ductile. For example, most of the metals are ductile. [/solution]...
Read More →Classify the following into elements,
[question] Question. Classify the following into elements, compounds and mixtures. (a) Sodium (b) Soil (c) Sugar solution (d) Silver (e) Calcium carbonate (f) Tin (g) Silicon (h) Coal (i) Air (j) Soap (k) Methane (l) Carbon dioxide (m) Blood [/question] [solution] Solution: Elements : sodium, silver, tin and silicon Compounds : calcium carbonate, soap, methane and carbon dioxide Mixtures : soil, sugar solution, coal, air and blood. [/solution]...
Read More →Give an example of a metal which
[question] Question. Give an example of a metal which (i) is a liquid at room temperature. (ii) can be easily cut with a knife. (iii) is the best conductor of heat. (iv) is a poor conductor of heat. [/question] [solution] solution: (i) Metal that exists in liquid state at room temperature – Mercury (ii) Metal that can be easily cut with a knife – Sodium (iii) Metal that is the best conductor of heat – Silver (iv) Metals that are poor conductors of heat –Mercury and lead [/solution]...
Read More →The following table gives the life times of neon lamps:
[question] Question. The following table gives the life times of neon lamps: (i) Represent the given information with the help of a histogram. (ii) How many lamps have a lifetime of more than 700 hours? [/question] [solution] Solution: (i) By taking life time (in hours) of neon lamps on x-axis and the number of lamps on y-axis, the histogram of the given information can be drawn as follows. Here, 1 unit on y-axis represents 10 lamps. (ii) It can be concluded that the number of neon lamps having ...
Read More →An army contingent of 616 members is to march behind an army band of 32 members in a parade
[question] Question. An army contingent of 616 members is to march behind an army band of 32 members in a parade. The two groups are to march in the same number of columns. What is the maximum number of columns in which they can march? [/question] [solution] Solution: 616 and 32 $616=32 \times 19+8$ $32=4 \times 8$ $\operatorname{HCF}$ of $(616,32)=8$ [/solution]...
Read More →Which of the following will show
[question] Question. Which of the following will show "Tyndall effect" ? (a) Salt solution (b) Milk (c) Copper sulphate solution (d) Starch solution [/question] [solution] Solution: Colloids show Tyndall effect, Milk is a colloid. Thus, it will show Tyndall effect. Therefore the correct answer is (b). [/solution]...
Read More →Give two important uses of washing
[question] Question. Give two important uses of washing soda and baking soda. [/question] [solution] solution: Two important uses of washing soda and baking soda are as follows- (1) Washing soda- (a) It is used in glass, soap, and paper industries. (b) It is used to remove permanent hardness of water. (2) Baking soda- (a) It is used as baking powder. Baking powder is a mixture of baking soda and a mild acid known as tartaric acid. When it is heated or mixed in water, it releases $\mathrm{CO}_{2}...
Read More →The length of 40 leaves of a plant are measured correct to one millimetre,
[question] Question. The length of 40 leaves of a plant are measured correct to one millimetre, and the obtained data is represented in the following table: (i) Draw a histogram to represent the given data. (ii) Is there any other suitable graphical representation for the same data? (iii) Is it correct to conclude that the maximum number of leaves are 153 mm long? Why? [/question] [solution] Solution: (i) It can be observed that the length of leaves is represented in a discontinuous class interv...
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