What are polyatomic ions
[question] Question. What are polyatomic ions? Give examples? [/question] [solution] Solution:\ A polyatomic ion is a group of atoms carrying a charge (positive or negative). For example, ammonium ion $\left(\mathrm{NH}_{4}^{+}\right)$, hydroxide ion $\left(\mathrm{OH}^{-}\right)$, carbonate ion $\left(\mathrm{CO}_{3}^{2-}\right)$, sulphate ion ( $\left.\mathrm{SO}_{4}^{2-}\right)$. [solution]...
Read More →Give reasons.
[question] Question. Give reasons. (a)Platinum, gold and silver are used to makejewellery. (b)Sodium, potassium and lithium are stored under oil. (c)Aluminium is a highly reactive metal, yet it is used to make utensils for cooking. (d)Carbonate and sulphide ores are usually converted into oxides during the process of extraction. [/question] [solution] solution: (a)Platinum, gold, and silver are used to make jewellery because they are very lustrous. Also, they are very less reactive and do not co...
Read More →Given that $\operatorname{HCF}(306,657)=9$, find $\operatorname{LCM}(306,657)$.
[question] Question. Given that $\operatorname{HCF}(306,657)=9$, find $\operatorname{LCM}(306,657)$. [/question] [solution] Solution: $\operatorname{LCM}(306,657)$ $=\frac{\mathbf{3 0 6} \times \mathbf{6 5 7}}{\mathbf{H C F}(\mathbf{3 0 6}, \mathbf{6 5 7})}=\frac{\mathbf{3 0 6} \times \mathbf{6 5 7}}{\mathbf{9}}=22338$ [/solution]...
Read More →Eleven bags of wheat flour, each marked 5 kg,
[question] Question. Eleven bags of wheat flour, each marked 5 kg, actually contained the following weights of flour (in kg): 4.97 5.05 5.08 5.03 5.00 5.06 5.08 4.98 5.04 5.07 5.00 Find the probability that any of these bags chosen at random contains more than 5 kg of flour. [/question] [solution] Solution: Number of total bags = 11 Number of bags containing more than 5 kg of flour = 7 Hence, required probability, $P=\frac{7}{11}$ [/solution]...
Read More →Find the LCM and HCF of the following integers by applying the prime factorisation method
[question] Question. Find the LCM and HCF of the following integers by applying the prime factorisation method (i) 12, 15 and 21 (ii) 17, 23 and 29 (iii) 8, 9 and 25 [/question] [solution] Solution: (i) 12,15 and 21 So, $12=2 \times 2 \times 3=2^{2} \times 3$ So, $15=3 \times 5$ So, $21=3 \times 7$ Therefore $\mathrm{HCF}(12,15,21)=3 ;$ $\mathrm{LCM}=(12,15,21)=2^{2} \times 3 \times 5 \times 7=420$ (ii) $17,23,29$ $17=1 \times 17$ $23=1 \times 23$ $29=1 \times 29$ $\mathrm{LCM}=1 \times 17 \time...
Read More →When 3.0 g of carbon is burnt in 8.00 g oxygen
[question] Question. When 3.0 g of carbon is burnt in 8.00 g oxygen, 11.00 g of carbon dioxide is produced. What mass of carbon dioxide will be formed when 3.00 g of carbon is burnt in 50.00 g of oxygen? Which law of chemical combinations will govern your answer? [/question] [solution] Solution: Carbon $+$ Oxygen $\rightarrow$ Carbon dioxide 3 g of carbon reacts with 8 g of oxygen to produce 11 g of carbon dioxide. If 3 g of carbon is burnt in 50 g of oxygen, then 3 g of carbon will react with 8...
Read More →What type of oxides is formed when non-metals
[question] Question. What type of oxides is formed when non-metals combine with oxygen? [/question] [solution] solution: Non-metals combine with oxygen to form acidic oxides. For example, [/solution]...
Read More →State two ways to prevent the
[question] Question. State two ways to prevent the rusting of iron. [/question] [solution] solution: Two ways to prevent the rusting of iron are- (i) Oiling, greasing, or painting- By applying oil, grease, or paint, the surface becomes water proof and the moisture and oxygen present in the air cannot come into direct contact with iron. Hence, rusting is prevented. (ii) Galvanisation - An iron article is coated with a layer of zinc metal, which prevents the iron to come in contact with oxygen and...
Read More →Note the frequency of two-wheelers,
[question] Question. Note the frequency of two-wheelers, three-wheelers and four-wheelers going past during a time interval, in front of your school gate. Find the probability that any one vehicle out of the total vehicles you have observed is a two-wheeler. [/question] [solution] Solution: This is an activity based question. Students are advised to perform this activity by yourself. [solution]...
Read More →A 0.24 g sample of compound of oxygen
[question] Question. A 0.24 g sample of compound of oxygen and boron was found by analysis to contain 0.096 g of boron and 0.144 g of oxygen. Calculate the percentage composition of the compound by weight. [/question] [solution] Solution: Mass of boron $=0.096 \mathrm{~g}$ (Given) Mass of oxygen $=0.144 \mathrm{~g}$ (Given) Mass of sample $=0.24 \mathrm{~g}$ (Given) Percentage of boron $=\frac{\text { Mass of boron }}{\text { Mass of sample }} \times 100$ $=\frac{0.096}{0.24} \times 100=40 \%$ P...
Read More →The distance (in km) of 40 engineers from their residence to their place of work were found as follows.
[question] Question. The distance (in km) of 40 engineers from their residence to their place of work were found as follows. What is the empirical probability that an engineer lives: (i) less than 7 km from her place of work? (ii) more than or equal to 7 km from her place of work? (iii) within $\frac{1}{2} \mathrm{~km}$ from her place of work? [solution] Solution: (i) Total number of engineers = 40 Number of engineers living less than 7 km from their place of work = 9 Hence, required probability...
Read More →Pratyush took sulphur powder on a spatula and heated it.
[question] Question. Pratyush took sulphur powder on a spatula and heated it. He collected the gas evolved by inverting a test tube over it, as shown in figure below. (a)What will be the action of gas on (i) dry litmus paper? (ii) moist litmus paper? (b)Write a balanced chemical equation for the reaction taking place. [/question] [solution] solution: (a)(i) There will be no action on dry litmus paper. (ii)Since the gas is sulphur dioxide $\left(\mathrm{SO}_{2}\right)$, it turns moist blue litmus...
Read More →To know the opinion of the students about the subject statistics,
[question] Question. To know the opinion of the students about the subject statistics, a survey of 200 students was conducted. The data is recorded in the following table. Find the probability that a student chosen at random (i) likes statistics, (ii) does not like it [/question] [solution] Solution: Total number of students = 135 + 65 = 200 (i) Number of students liking statistics = 135 $\mathrm{P}($ students liking statistics $)=\frac{135}{200}=\frac{27}{40}$ (ii) Number of students who do not...
Read More →Find the $\mathrm{LCM}$ and HCF of the following pairs of integers and verify that LCM $\times \mathrm{HCF}=$ product of two numbers.
[question] Question. Find the LCM and HCF of the following pairs of integers and verify that LCM $\times \mathrm{HCF}=$ product of two numbers. (i) 26 and 91 (ii) 510 and 92 (iii) 336 and 54 [/question] [solution] Solution: (i) 26 and 91 So, $26=2 \times 13$ So. $91=7 \times 13$ Therefore, $\operatorname{LCM}(26,91)=2 \times 7 \times 13=182$ $\operatorname{HCF}(26,91)=13$ Verification : LCM $\times$ HCF $=182 \times 13=2366$ and $26 \times 91=2366$ i.e., $\mathrm{LCM} \times \mathrm{HCF}=$ produ...
Read More →In the electrolytic refining of a metal M,
[question] Question. In the electrolytic refining of a metal M, what would you take as the anode, the cathode and the electrolyte ? [/question] [solution] solution: In the electrolytic refining of a metal M Anode – Impure metal M Cathode – Thin strip of pure metal M Electrolyte – Acidified solution of salt of the metal M [/solution]...
Read More →Which has more number of atoms,
[question] Question. Which has more number of atoms, 100 grams of sodium or 100 grams of iron (given, atomic mass of $\mathrm{Na}=23 \mathrm{u}, \mathrm{Fe}=56 \mathrm{u})$ ? [/question] [solution] Solution: 100 grams of sodium No. of sodium atoms $=\frac{\text { (Givenmass) }}{(\text { Gramatomic mass })} \times($ Avogadro's no. $)$ $=\frac{(100 g)}{(23 g)} \times\left(6.022 \times 10^{23}\right)=2.618 \times 10^{24}$ atoms 100 grams of iron No. of iron atoms $=\frac{\text { (Givenmass) }}{\tex...
Read More →Name two metals which will displace hydrogen from dilute acids,
[question] Question. Name two metals which will displace hydrogen from dilute acids, and two metals which will not. [/question] [solution] solution: Metals that are more reactive than hydrogen displace it from dilute acids. For example- sodium and potassium. Metals that are less reactive than hydrogen do not displace it. For example- copper and silver. [/solution]...
Read More →What are amphoteric oxides ?
[question] Question. What are amphoteric oxides ? Give two examples of amphoteric oxides. [/question] [solution] solution: Those oxides that behave as both acidic and basic oxides are called amphoteric oxides. Examples- Aluminium oxide $\left(\mathrm{Al}_{2} \mathrm{O}_{3}\right)$, Zinc oxide $(\mathrm{ZnO})$ [/solution]...
Read More →An organization selected 2400 families at random and surveyed them to determine a relationship between income level and the number of vehicles in a family.
[question] Question. An organization selected 2400 families at random and surveyed them to determine a relationship between income level and the number of vehicles in a family. The information gathered is listed in the table below: Suppose a family is chosen, find the probability that the family chosen is (i) earning Rs 10000 − 13000 per month and owning exactly 2 vehicles. (ii) earning Rs 16000 or more per month and owning exactly 1 vehicle. (iii) earning less than Rs 7000 per month and does no...
Read More →If one mole of carbon atoms weighs
[question] Question. If one mole of carbon atoms weighs 12 gram, what is the mass (in gram) of 1 atom of carbon? [question] [solution] Solution: One mole of carbon atoms weighs $12 \mathrm{~g}$ (Given) i.e., mass of 1 mole of carbon atoms = 12 g One atom of carbon has mass $=12 \mathrm{~g} \times \frac{1}{6.022 \times 10^{23}}=1.99 \times 10^{-23} \mathrm{~g}$ [/solution]...
Read More →You are given a hammer,
[question] Question. You are given a hammer, a battery, a bulb, wires and a switch. (a) How could you use them to distinguish between samples of metals and non-metals? (b) Assess the usefulness of these tests in distinguishing between metals and non-metals. [/question] [solution] solution: (a)With the hammer, we can beat the sample and if it can be beaten into thin sheets (that is, it is malleable), then it is a metal otherwise a non metal. Similarly, we can use the battery, bulb, wires, and a s...
Read More →Three coins are tossed simultaneously 200 times with the following frequencies of different outcomes
[question] Question. Three coins are tossed simultaneously 200 times with the following frequencies of different outcomes If the three coins are simultaneously tossed again, compute the probability of 2 heads coming up. [/question] [solution] Solution: Number of times 2 heads come up = 72 Total number of times the coins were tossed = 200 $P(2$ heads will come up $)=\frac{\text { Number of times } 2 \text { heads come up }}{\text { Total number of times the coins were tossed }}$ $=\frac{72}{200}=...
Read More →Calculate the molecular masses
[question] Question. Calculate the molecular masses of $\mathrm{H}_{2}, \mathrm{O}_{2}, \mathrm{Cl}_{2}, \mathrm{CO}_{2}, \mathrm{CH}_{4}, \mathrm{C}_{2} \mathrm{H}_{6}, \mathrm{C}_{2} \mathrm{H}_{4}, \mathrm{NH}_{3}, \mathrm{CH}_{3} \mathrm{OH}$. [/question] [solution] Solution: Molecular mass of $\mathrm{H}_{2}=2 \times$ Atomic mass $(\mathrm{H})$ $=2 \times 1=2 \mathrm{u}$ Molecular mass of $\mathrm{O}_{2}=2 \times$ Atomic mass $(\mathrm{O})$ $=2 \times 16=32 \mathrm{u}$ Molecular mass of $\m...
Read More →Food cans are coated with tin and not with zinc because
[question] Question. Food cans are coated with tin and not with zinc because (a)zinc is costlier than tin. (b)zinc has a higher melting point than tin. (c)zinc is more reactive than tin. (d)zinc is less reactive than tin. [/question] [solution] solution: (c)Food cans are coated with tin and not with zinc because zinc is more reactive than tin. [/solution]...
Read More →An element reacts with oxygen to give a compound with a high melting point.
[question] Question. An element reacts with oxygen to give a compound with a high melting point. This compound is also soluble in water. The element is likely to be (a) Calcium (b) Carbon (c) Silicon (d) Iron [/question] [solution] solution: (a) The element is likely to be calcium [/solution]...
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