Which of the following methods is suitable for preventing
[question] Question. Which of the following methods is suitable for preventing an iron frying pan from rusting? (a) Applying grease (b) Applying paint (c) Applying a coating of zinc (d) all of the above. [/question] [solution] solution: (c) Applying a coating of zinc (We can also apply grease and paint to prevent iron from rusting. However, in case of iron frying pan, grease and paint cannot be applied because when the pan will be heated and washed again and again, the coating of grease and pain...
Read More →Which of the following pairs will
[question] Question. Which of the following pairs will give displacement reactions ? (a) NaCl solution and copper metal (b) $\mathrm{MgCl}_{2}$ solution and aluminium metal (c) $\mathrm{FeSO}_{4}$ solution and silver metal (d) $\mathrm{AgNO}_{3}$ solution and copper metal. [/question] [solution] solution: (d) $\mathrm{AgNO}_{3}$ solution and copper metal [/solution]...
Read More →In a particular section of Class IX,
[question] Question. In a particular section of Class IX, 40 students were asked about the months of their birth and the following graph was prepared for the data so obtained: Find the probability that a student of the class was born in August. [/question] [solution] Solution: Number of students born in the month of August = 6 Total number of students = 40 P $($ Students born in the month of August $)=\frac{\text { Number of students born in August }}{\text { Total number of students }}$ $=\frac...
Read More →How many atoms a
[question] Question. How many atoms are present in a (i) $\mathrm{H}_{2} \mathrm{~S}$ molecule and (ii) $\mathrm{PO}_{4}^{3}$ ion? [/question] [solution] Solution: (i) In a $\mathrm{H}_{2} \mathrm{~S}$ molecule, three atoms are present; two of hydrogen and one of sulphur. (ii) In a $\mathrm{PO}_{4}^{3-}$ ion, five atoms are present; one of phosphorus and four of oxygen [/solution]...
Read More →1500 families with 2 children were selected randomly,
[question] Question. 1500 families with 2 children were selected randomly, and the following data were recorded: Compute the probability of a family, chosen at random, having (i) 2 girls (ii) 1 girl (iii) No girl Also check whether the sum of these probabilities is 1. [/question] [solution] Solution: Total number of families = 475 + 814 + 211 = 1500 (i) Number of families having 2 girls $=475$ $P_{1}($ a randomly chosen family has 2 girls $)=\frac{\text { Number of families having } 2 \text { gi...
Read More →What are alloys ?
[question] Question. What are alloys ? [solution] solution: Alloys are homogeneous mixtures of two or more elements. The elements could be two metals, or a metal and a non-metal. An alloy is formed by first melting the metal and then dissolving the other elements in it. For example, steel is an alloy of iron and carbon. [/solution]...
Read More →Which metals do not corrode
[question] Question. Which metals do not corrode easily ? [/question] [solution] solution: More reactive a metal is, more likely it is to be corroded. Therefore, less reactive metals are less likely to get corroded. This is why gold plating provides high resistance to corrosion. [/solution]...
Read More →What is meant by the term
[question] Question. What is meant by the term chemical formula? [/question] [solution] Solution: The chemical formula of a compound means the symbolic representation of the composition of a compound. For example, from the chemical formula CO2 of carbon dioxide, we come to know that one carbon atom and two oxygen atoms are chemically bonded together to form one molecule of the compound, carbon dioxide. [/solution]...
Read More →In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays.
[question] Question. In a cricket math, a batswoman hits a boundary 6 times out of 30 balls she plays. Find the probability that she did not hit a boundary. [/question] [solution] Solution: Number of times the batswoman hits a boundary = 6 Total number of balls played = 30 ā“ Number of times that the batswoman does not hit a boundary = 30 ā 6 = 24 $P($ she does not hit a boundary $)=\frac{\text { Number of times when she does not hit boundary }}{\text { Total number of balls played }}$ $=\frac{24...
Read More →Metallic oxides of zinc, magnesium and copper
[question] Question. Metallic oxides of zinc, magnesium and copper were heated with the following metals. In which cases will you find displacement reactions taking place? [solution] solution: [/solution]...
Read More →Give one example of a situation in which
[question] Question. Give one example of a situation in which (i) The mean is an appropriate measure of central tendency. (ii) The mean is not an appropriate measure of central tendency but the median is an appropriate measure of central tendency. [/question] [solution] Solution: When any data has a few observations such that these are very far from the other observations in it, it is better to calculate the median than the mean of the data as median gives a better estimate of average in this ca...
Read More →Write down the names of compounds
[question] Question. (i) $\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}$ (ii) $\mathrm{CaCl}_{2}$ (iii) $\mathrm{K}_{2} \mathrm{SO}_{4}$ (iv) $\mathrm{KNO}_{3}$ (v) $\mathrm{CaCO}_{3}$ [/question] [solution] Solution: (i) $\mathrm{Al}_{2}\left(\mathrm{SO}_{4}\right)_{3}$ : Aluminium sulphate (ii) $\mathrm{CaCl}_{2}$ : Calcium chloride (iii) $\mathrm{K}_{2} \mathrm{SO}_{4}$ : Potassium sulphate (iv) $\mathrm{KNO}_{3}$ : Potassium nitrate (v) $\mathrm{CaCO}_{3}$ : Calcium carbonate [/solution]...
Read More →What chemical process is used for obtaining
[question] Question. What chemical process is used for obtaining a metal from its oxide ? [/question] [solution] solution: The chemical process used for obtaining a metal from its oxide is reduction. In this process, metal oxides are reduced by using suitable reducing agents such as carbon or by using highly reactive metals to displace the metals from their oxides. For example, zinc oxide is reduced to metallic zinc by heating with carbon. $\mathrm{ZnO}(\mathrm{s})+\mathrm{C}(\mathrm{s}) \stackr...
Read More →Find the mean salary of 60 workers of a factory from the following table:
[question] Question. Find the mean salary of 60 workers of a factory from the following table: [/question] [solution] Solution: We know that Mean $=\frac{\sum f_{i} x_{i}}{\sum f_{i}}$ The value of $\sum f_{i} x_{i}$ and $\sum f_{i}$ can be calculated as follows. Mean salary $=\frac{305000}{60}$ $=5083.33$ Therefore, mean salary of 60 workers is Rs 5083.33. [/solution]...
Read More →Write down the formulae of
[question] Question. (i) sodium oxide (ii) aluminium chloride (iii) sodium sulphide (iv) magnesium hydroxide [question] [solution] Solution: (i) Sodium oxide : $\mathrm{Na}_{2} \mathrm{O}$ (ii) Aluminium chloride : $\mathrm{AlCl}_{3}$ (iii) Sodium suphide : $\mathrm{Na}_{2} \mathrm{~S}$ (iv) Magnesium hydroxide : $\mathrm{Mg}(\mathrm{OH})_{2}$ [/solution]...
Read More →Name two metals which are
[question] Question. Name two metals which are found in nature in the free state. [/question] [solution] solution: The metals at the bottom of the reactivity series are mostly found in free state. For examplegold, silver, and platinum. [/solution]...
Read More →Express each number as product of its prime factors :
[question] Question. Express each number as product of its prime factors : (i) 140 (ii) 156 (iii) 3825 (iv) 5005 (v) 7429 [/question] [solution] Solution: (i) 140 So, $140=2 \times 2 \times 5 \times 7=2^{2} \times 5 \times 7$ (ii) 156 So, $156=2 \times 2 \times 3 \times 13=2^{2} \times 3 \times 13$ So, $3825=3^{2} \times 5^{2} \times 17$ (iv) 5005 So, $5005=5 \times 7 \times 11 \times 13$ (v) 7429 So, $7429=17 \times 19 \times 23$ [/solution]...
Read More →Find the mode of 14, 25, 14, 28, 18, 17, 18, 14, 23, 22, 14, 18.
[question] Question. Find the mode of 14, 25, 14, 28, 18, 17, 18, 14, 23, 22, 14, 18. [/question] [solution] Solution: Arranging the data in an ascending order, 14, 14, 14, 14, 17, 18, 18, 18, 22, 23, 25, 28 It can be observed that 14 has the highest frequency, i.e. 4, in the given data. Therefore, mode of the given data is 14. [/solution]...
Read More →Define the following terms.
[question] Question. Define the following terms. (i) Mineral (ii) Ore (iii) Gangue [/question] [solution] solution: (i) Mineral: Most of the elements occur in nature in combined state as minerals. The chemical composition of minerals is fixed. (ii) Ore : Minerals from which metals can be extracted profitably are known as ores. (iii) Gangue: The impurities (sand, silt, soil, gravel,etc.) present in the ore are called gangue. [/solution]...
Read More →Why is it not possible to see an atom
[question] Question. Why is it not possible to see an atom with naked eyes? [/question] [solution] Solution: The size of an atom is too small thats why it is not possible to see it with naked eyes [/solution]...
Read More →Define atomic mass unit?
[question] Question. Define atomic mass unit. [/question] [solution] Solution: Atomic mass unit equal to exactly one-twelth the mass of one atom of carbon-12 is called one atomic mass unit. It is written as āuā. [/solution]...
Read More →Why do ionic compounds have high
[question] Question. Why do ionic compounds have high melting points? [/question] [solution] solution: Ionic compounds have strong electrostatic forces of attraction between the ions. Therefore, it requires a lot of energy to overcome these forces. That is why ionic compounds have high melting points. [/solution]...
Read More →The following observations have been arranged in ascending order.
[question] Question. The following observations have been arranged in ascending order. If the median of the data is 63, find the value of x. 29, 32, 48, 50, x, x + 2, 72, 78, 84, 95 [/question] [solution] Solution: It can be observed that the total number of observations in the given data is 10 (even number). Therefore, the median of this data will be the mean of $\frac{10}{2}$ i.e., $5^{\text {th }}$ and $\frac{10}{2}+1$ i.e., $6^{\text {th }}$ observation. Therefore, median of data $=\frac{5^{...
Read More →(i) Write the electron-dot structures for sodium, oxygen and magnesium.
[question] Question. (i) Write the electron-dot structures for sodium, oxygen and magnesium. (ii) Show the formation of $\mathrm{Na}_{2} \mathrm{O}$ and $\mathrm{MgO}$ by the transfer of electrons. (iii) What are the ions present in these compounds? [/question] [solution] solution: (i) The representation of elements with valence electrons as dots around the elements is referred to as electron-dot structure for elements. (iii) The ions present in $\mathrm{Na}_{2} \mathrm{O}$ are $\mathrm{Na}^{+}$...
Read More →In a mathematics test given to 15 students,
[question] Question. In a mathematics test given to 15 students, the following marks (out of 100) are recorded: 41, 39, 48, 52, 46, 62, 54, 40, 96, 52, 98, 40, 42, 52, 60 Find the mean, median and mode of this data. [/question] [solution] Solution: The marks of 15 students in mathematics test are 41, 39, 48, 52, 46, 62, 54, 40, 96, 52, 98, 40, 42, 52, 60 Mean of data $=\frac{\text { Sum of all observation }}{\text { Total number of observation }}$ $=\frac{41+39+48+52+46+62+54+40+96+52+98+40+42+5...
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