NCERT Exemplar

Answer the following and justify: (iii) If on division of a polynomial p (x) by a polynomial g (x), the quotient is zero, what is the relation between the degrees of p (x) and g (x)? (iv) If on division of a non-zero polynomial p (x) by a polynomial g (x), the remainder is zero, what is the relation between the degrees of p (x) and g (x)?

(iii) If on division of a polynomial p (x) by a polynomial g (x), the remainder is zero, what is the connection between the levels of p (x) and g (x)? We realize that, \[p\left( x \right)=\text{...

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We wish to obtain an erect image of an object, using a concave mirror of focal length 15 cm. What should be the range of distance of the object from the mirror? What is the nature of the image? Is the image larger or smaller than the object? Draw a ray diagram to show the image formation in this case.

Answer- The object's distance from the mirror's pole ranges from 0 to 15 cm. The image's nature is virtual, upright, and larger than the thing.

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A convex lens forms a real and inverted image of a needle at a distance of 50 cm from it. Where is the needle placed in front of the convex lens if the image is equal to the size of the object? Also, find the power of the lens.

Answer- Because the image is actual and the same size, it should be positioned at 2F. The image of the needle is assumed to be formed at a distance of 50 cm from the convex lens. As a result, the...

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A farmer connects a pipe of internal diameter 20 cm from a canal into a cylindrical tank in her field, which is 10 m in diameter and 2 m deep. If water flows through the pipe at the rate of 3 km/h, in how much time will the tank be filled?

Think about the accompanying graph Volume of water that streams in t minutes from pipe \[=\text{ }t\times 0.5\pi \text{ }m^3\] Volume of water that streams in t minutes from pipe = \[t\times 0.5\pi...

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In the double displacement reaction between aqueous potassium iodide and aqueous lead nitrate, a yellow precipitate of lead iodide is formed. While performing the activity if lead nitrate is not available, which of the following can be used in place of lead nitrate?
(a) Lead sulphate (insoluble)
(b) Lead acetate
(c) Ammonium nitrate
(d) Potassium sulphate

Solution: The correct response is (b) lead acetate. Explanation: Because we need a compound that contains lead in order to obtain lead iodide, ammonium nitrate and potassium sulphate are ruled out....

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Barium chloride on reacting with ammonium sulphate forms barium sulphate and ammonium chloride. Which of the following correctly represents the type of the reaction involved?
(i) Displacement reaction
(ii) Precipitation reaction
(iii) Combination reaction
(iv) Double displacement reaction
(a) (i) only
(b) (ii) only
(c) (iv) only
(d) (ii) and (iv)

Solution: Answer is option d) The elements ammonium and barium are being displaced from their respective salts, according to the data. As a result, we have a double displacement reaction. Because of...

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Which among the following statement(s) is (are) true? Exposure of silver chloride to sunlight for a long duration turns grey due to
(i) the formation of silver by decomposition of silver chloride
(ii) sublimation of silver chloride
(iii) decomposition of chlorine gas from silver chloride
(iv) oxidation of silver chloride
(a) (i) only
(b) (i) and (iii)
(c) (ii) and (iii)
(d) (iv) only

Solution: Answer is option a) Silver halides, particularly silver chloride, decompose in the presence of sunlight, resulting in the formation of silver metal and a halogen gas (silver) (chlorine or...

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Solid calcium oxide reacts vigorously with water to form calcium hydroxide accompanied by the liberation of heat. This process is called slaking of lime. Calcium hydroxide dissolves in water to form its solution called lime water. Which among the following is (are) true about slaking of lime and the solution formed?
(i) It is an endothermic reaction
(ii) It is an exothermic reaction
(iii) The pH of the resulting solution will be more than seven
(iv) The pH of the resulting solution will be less than seven
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)

Solution: The answer is (b) (ii) and (iii) In the presence of vigorous water reaction, solid calcium oxide transforms into calcium hydroxide, which is accompanied by the production of heat. This...

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Which among the following is(are) double displacement reaction(s)?
(i) Pb + CuCl2 → PbCl2 + Cu
(ii) Na2 SO4 + BaCl2 → BaSO4 + 2NaCl
(iii) C + O2 → CO2
(iv) CH4 + 2O2 → CO2 + 2H2O
(a) (i) and (iv)
(b) (ii) only
(c) (i) and (ii)
(d) (iii) and (iv)

Solution: The answer is (b) (ii) only Sodium and barium are both displaced from their respective salts in this reaction, which is referred to as a double displacement reaction.

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A dilute ferrous sulphate solution was gradually added to the beaker containing acidified permanganate solution. The light purple colour of the solution fades and finally disappears. Which of the following is the correct explanation for the observation?
(a) KMnO4 is an oxidising agent, it oxidises FeSO4
(b) FeSO4 acts as an oxidising agent and oxidises KMnO4
(c) The colour disappears due to dilution; no reaction is involved
(d) KMnO4 is an unstable compound and decomposes in the presence of FeSO4 to a colourless compound.

Solution: Answer is (a) KMnO4 is an oxidising agent, it oxidises FeSO4 Potassium permanganate (KMnO4) is used as an oxidising agent during this reaction. This is due to the presence of KMnO4, which...

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Three beakers labelled as A, B and C each containing 25 mL of water were taken. A small amount of NaOH, anhydrous CuSO4 and NaCl were added to the beakers A, B and C respectively. It was observed that there was an increase in the temperature of the solutions contained in beakers A and B, whereas, in the case of beaker C, the temperature of the solution falls. Which one of the following statements(s) is(are) correct?
(i) In beakers A and B, the exothermic process has occurred.
(ii) In beakers A and B, the endothermic process has occurred.
(iii) In beaker C exothermic process has occurred.
(iv) In beaker C endothermic process has occurred.
(a) (i) only
(b) (ii) only
(c) (i) and (iv)
(d) (ii) and (iii)

Answer: Answer is (c) (i) and (iv) Exothermic processes result in the release of enormous amounts of heat – as a result, when water reacts with quick lime and when acid reacts with water, heat...

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Which of the following are exothermic processes?
(i) The reaction of water with quick lime
(ii) Dilution of an acid
(iii) Evaporation of water
(iv) Sublimation of camphor (crystals)
(a) (i) and (ii)
(b) (ii) and (iii)
(c) (i) and (iv)
(d) (iii) and (iv)

Answer: Option a) Exothermic processes result in the release of enormous amounts of heat – as a result when water reacts with quick lime and when an acid reacts with water, heat energy is...

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Which of the following statements about the given reaction are correct? 3Fe(s) + 4H2O(g) → Fe3O4 (s) + 4H2 (g)
1. Iron metal is getting oxidised
2. Water is getting reduced
3. Water is acting as a reducing agent
4. Water is acting as an oxidising agent
(a) (i), (ii) and (iii)
(b) (iii) and (iv)
(c) (i), (ii) and (iv)
(d) (ii) and (iv)

Answer: Option c) In this reaction, oxygen reacts with water to form oxidised water. Because oxygen is being removed from water, the water's oxygen content is being reduced. Water is a source of...

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The following reaction is an example of a:4NH3 (g) + 5O2 (g) → 4NO(g) + 6H2O(g)
(i) displacement reaction
(ii) combination reaction
(iii) redox reaction
(iv) neutralisation reaction
(a) (i) and (iv)
(b) (ii) and (iii)
(c) (i) and (iii)
(d) (iii) and (iv)

Solution: Answer is (c)  (i) and (iii) The reaction described here is a combination of displacement and redox reactions. The displacement reaction occurs when oxygen displaces hydrogen in ammonia,...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(c) Ethanol is warmed with ethanoic acid to form ethyl acetate in the presence of concentrated H_2SO_4
(d) Ethene is burnt in the presence of oxygen to form carbon dioxide, water and releases heat and light.

Answer: (c) $C_2 H_5 OH ( aq )+ CH_3 COOH (l) \longrightarrow CH_3 COO C_2 H_5( aq )+ H_2 O ( t )$It is a neutralisation reaction and double displacement reaction.(d) $C_{2} H_{4}( g )+3 O_{2}(g)...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas.
(b) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.

Answer: (a) $N {2}( g )+3 H {2}( g )=\frac{\text { catalyst }}{773 K } 2 NH {2}( g )$ It is a combination reaction. (b) $NaOH ( aq )+ CH _{3} COOH ( aq ) \longrightarrow CH_3 COONa ( aq )+ H_2 O...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat.

Answer: c) Aqueous potassium iodide solution is passed through a chlorine gas stream, resulting in the formation of potassium chloride solution and solid iodine.This is a reaction with a single...

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Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.

Answer: a) Iron (III) oxide reacts with aluminium to form molten iron and aluminium oxide in the first step of the Thermit reaction. This is a reaction with a single displacement. Fe2O3 + 2Al →...

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During the reaction of some metals with dilute hydrochloric acid, the following observations were made.
(a) Silver metal does not show any change
(b) The temperature of the reaction mixture rises when aluminum (Al) is added.

Answer: a) Because silver is a member of the low reactive series of metals, there will be no reaction between it and dilute hydrogen chloride. b) Due to the fact that it is an exothermic reaction,...

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During the reaction of some metals with dilute hydrochloric acid, the following observations were made.
(c) The reaction of sodium metal is found to be highly explosive
d) Some bubbles of gas are seen when lead (Pb) is reacted with the acid.

Answer: c) Sodium is a highly reactive metal, and when it reacts with atmospheric oxygen, it produces an exothermic reaction, which raises the temperature of the surrounding environment. d) Hydrogen...

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A substance X, which is an oxide of a group 2 element, is used intensively in the cement industry. This element is present in bones also. On treatment with water, it forms a solution that turns red litmus blue. Identify X and also write the chemical reactions involved.

Answer: Calcium oxide is the chemical compound X. CaO is a compound that is widely used in the cement industry. Water treatment of CaO results in the formation of Ca(OH)2, which is alkaline in...

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Write a balanced chemical equation for each of the following reactions and also classify them.
(c) Iron (III) oxide on heating with carbon monoxide gas reacts to form solid iron and liberates carbon dioxide gas.
(d) Hydrogen sulfide gas reacts with oxygen gas to form solid sulfur and liquid water.

Answer: (c) Fe2O3 + 3CO + 2Fe + 3CO2 This is a redox reaction. (d) 2 H2S+O2 → 2 s + 2 H2O This is a replacement reaction.

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Write a balanced chemical equation for each of the following reactions and also classify them.
(a) Lead acetate solution is treated with dilute hydrochloric acid to form lead chloride and acetic acid solution.
(b) A piece of sodium metal is added to absolute ethanol to form sodium ethoxide and hydrogen gas.

Answer: (a) Pb(CH3COO)2 + 2HCI – PbCl2 + CH3COOH This is a Double Displacement reaction. (b) 2Na + 2C2H5OH + 2C2H5ONa+ H2 This is a Displacement reaction.

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A magnesium ribbon is burnt in oxygen to give a white compound X accompanied by the emission of light. If the burning ribbon is now placed in an atmosphere of nitrogen, it continues to burn and forms a compound Y.
(a) Write the chemical formulae of X and Y.
(b) Write a balanced chemical equation, when X is dissolved in water.

Solution: a) It is formed when magnesium ribbon is burned in oxygen with the emission of light and heat energy that magnesium oxide is formed.X is a compound with the chemical formula MgO. After...

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A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining. (a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved. (b) Name the black substance formed and give its chemical formula.

Solution: A reaction between silver and H2S in the atmosphere results in the formation of Silver Sulphide, which is a dark brown compound with a sulfuric acid smell. Corrosion is the term used to...

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On heating blue colored powder of copper (II) nitrate in a boiling tube, copper oxide (black), oxygen gas and a brown gas X are formed
(c) Identify the type of reaction.
(d) What could be the pH range of the aqueous solution of the gas X?

Answer: c) Thermal decomposition is the reaction that is taking place. d) Due to the fact that NO2 dissolves in water and forms an acidic solution, pH is less than 7. (pH range below 7).

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