Mix Examples - Acids, Bases and Salts Questions in English

(N/A) $(i)$ The reaction of zinc metal with dilute hydrochloric acid produces zinc chloride and hydrogen gas: $Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)$.
$(ii)$ The reaction of sodium carbonate with dilute hydrochloric acid produces sodium chloride,water,and carbon dioxide gas: $Na_{2}CO_{3}(s) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_{2}O(l) + CO_{2}(g)$.
$(iii)$ The reaction of sodium hydroxide (a base) with dilute hydrochloric acid (an acid) is a neutralization reaction producing sodium chloride and water: $NaOH(aq) + HCl(aq) \rightarrow NaCl(aq) + H_{2}O(l)$.

(N/A) $(i)$ The products obtained in the chlor-alkali process are chlorine gas $(Cl_2)$,hydrogen gas $(H_2)$,and sodium hydroxide $(NaOH)$ solution.
$(ii)$ Chlorine gas $(Cl_2)$ is liberated at the anode,and hydrogen gas $(H_2)$ is liberated at the cathode.
$(iii)$ The solution used as raw material in this process is brine,which is an aqueous solution of sodium chloride $(NaCl)$.

(N/A) $Ca(OH)_{2} + Cl_{2} \longrightarrow CaOCl_{2} + H_{2}O$ (Bleaching powder is formed).
$(b)$ $CaSO_{4} \cdot 1/2 H_{2}O + 1 \frac{1}{2} H_{2}O \longrightarrow CaSO_{4} \cdot 2H_{2}O$ (Gypsum is formed).
$(c)$ $Na_{2}CO_{3} \cdot 10H_{2}O \xrightarrow{\text{air}} Na_{2}CO_{3} \cdot H_{2}O + 9H_{2}O$ (Efflorescence occurs,forming sodium carbonate monohydrate).

(N/A) $(i)$ Ants contain formic acid (also known as methanoic acid).
$(ii)$ Lemon contains citric acid.
$(iii)$ Milk contains lactic acid.
$(iv)$ Tomato contains oxalic acid.

(N/A) $(i)$ Sodium carbonate $(Na_{2}CO_{3})$
(ii) Sodium sulphate $(Na_{2}SO_{4})$

(N/A) Copper sulphate pentahydrate $(CuSO_4 \cdot 5H_2O)$ crystals are blue due to the presence of $5$ molecules of water of crystallisation. On heating, they lose these water molecules and become anhydrous copper sulphate $(CuSO_4)$, which is white in colour.
$(b)$ Baking soda $(NaHCO_3)$ is mildly alkaline in nature. When taken, it reacts with the excess hydrochloric acid $(HCl)$ produced in the stomach, neutralising it and providing relief from acidity.
$(c)$ The process of diluting a concentrated acid is highly exothermic. If water is added to a concentrated acid, the large amount of heat generated can cause the mixture to splash out, potentially causing severe acid burns. Therefore, acid is always added to water slowly with constant stirring.

(N/A) The colour of the solution becomes blue-green and the copper oxide dissolves. The chemical reaction is: $CuO + 2HCl \rightarrow CuCl_2 + H_2O$.
$(b)$ Aqueous solution of $HCl$ dissociates to produce $H^+$ ions,which are responsible for its acidic character. However,glucose $(C_6H_{12}O_6)$ is a covalent compound that does not dissociate into ions in water; therefore,it does not produce $H^+$ ions and fails to show acidic character.

(N/A) Curd and other sour substances contain acids.
These acids react with the metal (copper) present in brass and copper vessels.
This chemical reaction leads to the formation of metallic salts (compounds) which are toxic or poisonous in nature.
Consuming food stored in such vessels can cause food poisoning.

(N/A) When chlorine is passed over dry slaked lime $(Ca(OH)_2)$,it forms bleaching powder $(CaOCl_2)$ and water $(H_2O)$. The balanced equation is: $Ca(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O$
$(b)$ When sodium bicarbonate $(NaHCO_3)$ reacts with dilute hydrochloric acid $(HCl)$,it produces sodium chloride $(NaCl)$,water $(H_2O)$,and carbon dioxide $(CO_2)$. The balanced equation is: $NaHCO_3 + HCl \rightarrow NaCl + H_2O + CO_2$
$(c)$ When sodium bicarbonate $(NaHCO_3)$ is heated,it undergoes thermal decomposition to form sodium carbonate $(Na_2CO_3)$,water $(H_2O)$,and carbon dioxide $(CO_2)$. The balanced equation is: $2NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2$

(N/A) universal indicator is a mixture of several indicators that exhibits different colours at different concentrations of hydrogen ions in a solution,allowing for the determination of the $pH$ value.
$(b)$ The process is known as the Chlor-alkali process. The chemical equation is: $2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g)$.

(N/A) The chemical formula of hydrated copper sulphate is $CuSO_4 \cdot 5H_2O$ (blue vitriol),and anhydrous copper sulphate is $CuSO_4$ (white).
Activity: Take some copper sulphate crystals in a dry boiling tube and heat them. The blue colour of the crystals disappears,and the substance becomes white due to the loss of water of crystallisation. If we add a few drops of water to this anhydrous copper sulphate,the blue colour is restored.
$(b)$ Plaster of Paris: Calcium sulphate hemihydrate,$CaSO_4 \cdot \frac{1}{2}H_2O$.
Gypsum: Calcium sulphate dihydrate,$CaSO_4 \cdot 2H_2O$.

(N/A) $(i) \text{ } CaOCl_2(s) + CO_2(g) \to CaCO_3(s) + Cl_2(g)$
$(ii) \text{ } CuSO_4 \cdot 5H_2O(s) \xrightarrow{\text{Heat}} CuSO_4(s) + 5H_2O(g)$
$(iii) \text{ } Ca(OH)_2(s) + Cl_2(g) \to CaOCl_2(s) + H_2O(l)$

(N/A) $(i)$ $Ca(OH)_2(aq) + CO_2(g) \to CaCO_3(s) + H_2O(l)$
(Lime water turns milky due to the formation of insoluble calcium carbonate.)
$(ii)$ $2NaOH(aq) + Zn(s) \xrightarrow{\text{Heat}} Na_2ZnO_2(aq) + H_2(g)$
(Sodium zincate is formed along with the evolution of hydrogen gas.)

(A) Vigorous reaction will be seen in test tube $A$.
$(b)$ This is because $H_{2}SO_{4}$ is a strong acid,whereas $H_{2}CO_{3}$ is a weak acid.
$(c)$ $(i)$ Hydrogen gas $(H_{2})$ is liberated in both test tubes.
$(ii)$ When a burning candle is brought near the evolving gas,it burns with a 'pop' sound. This confirms the presence of hydrogen gas.

(B) The chemical equations for the reactions are:
$Mg(s) + H_{2}SO_{4}(aq) \rightarrow MgSO_{4}(aq) + H_{2}(g)$
$Mg(s) + H_{2}CO_{3}(aq) \rightarrow MgCO_{3}(s) + H_{2}(g)$
$(b)$ $H_{2}SO_{4}$ is a strong acid,while $H_{2}CO_{3}$ is a weak acid.
Therefore,$H_{2}SO_{4}$ will have a lower $pH$ value because it dissociates completely to provide a higher concentration of $H^{+}$ ions.
Conversely,$H_{2}CO_{3}$ will have a lower $H^{+}$ concentration because it is a weak acid and dissociates only partially.

(N/A) Metal carbonates and metal hydrogen carbonates react with acids to produce the corresponding salt,carbon dioxide,and water.
$(b)$ Chemical equations:
$(i)$ Metal carbonate: $Na_{2}CO_{3}(s) + 2HCl(aq) \rightarrow 2NaCl(aq) + H_{2}O(l) + CO_{2}(g)$
$(ii)$ Metal hydrogen carbonate: $NaHCO_{3}(s) + HCl(aq) \rightarrow NaCl(aq) + H_{2}O(l) + CO_{2}(g)$
$(c)$ The gas evolved during the reaction is carbon dioxide $(CO_{2})$.
$(d)$ When carbon dioxide gas is passed through lime water $(Ca(OH)_{2})$,it turns milky due to the formation of white precipitate of calcium carbonate $(CaCO_{3})$.

(N/A) $Zn(s) + H_{2}SO_{4}(aq) \rightarrow ZnSO_{4}(aq) + H_{2}(g)$
$(b)$ $Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)$
$(c)$ $3Zn(s) + 2AlCl_{3}(aq) \rightarrow 3ZnCl_{2}(aq) + 2Al(s)$ (Zinc is more reactive than Aluminium,so it displaces it)
$(d)$ $Zn(s) + 2NaOH(aq) \rightarrow Na_{2}ZnO_{2}(aq) + H_{2}(g)$ (Formation of Sodium zincate)
$(e)$ $4Zn(s) + 10HNO_{3}(dilute) \rightarrow 4Zn(NO_{3})_{2}(aq) + NH_{4}NO_{3}(aq) + 3H_{2}O(l)$

(A) : Hydrated copper sulphate $(CuSO_4 \cdot 5H_2O)$
$B$: Water of crystallisation $(H_2O)$
$C$: Anhydrous copper sulphate $(CuSO_4)$
$D$: Water $(H_2O)$
$(b)$ The chemical equations are:
$CuSO_4 \cdot 5H_2O (s) \xrightarrow{\text{Heat}} CuSO_4 (s) + 5H_2O (g)$
(Blue) (White)
$CuSO_4 (s) + 5H_2O (l) \rightarrow CuSO_4 \cdot 5H_2O (s)$
(White) (Blue)
$(c)$ Another salt that shows this property is Ferrous sulphate $(FeSO_4 \cdot 7H_2O)$,which is green in colour and turns white upon heating due to the loss of water of crystallisation.

(N/A) Chemical name: Sodium carbonate decahydrate.
Formula: $Na_{2}CO_{3} \cdot 10H_{2}O$
$(b)$ It is obtained via the Solvay process:
$NaCl + H_{2}O + CO_{2} + NH_{3} \rightarrow NH_{4}Cl + NaHCO_{3}$
$2NaHCO_{3} \xrightarrow{\Delta} Na_{2}CO_{3} + CO_{2} \uparrow + H_{2}O$
$Na_{2}CO_{3} + 10H_{2}O \rightarrow Na_{2}CO_{3} \cdot 10H_{2}O$
$(c)$ It is called a basic salt because it is a salt of a strong base $(NaOH)$ and a weak acid $(H_{2}CO_{3})$,which makes its aqueous solution alkaline.
Use: It is used for removing permanent hardness of water.

(N/A) The common salt used in food is sodium chloride $(NaCl)$. It is formed by the combination of hydrochloric acid $(HCl)$ and sodium hydroxide $(NaOH)$. The primary source of common salt is seawater (ocean water).
$(b)$ Rock salt refers to large deposits of solid salt found in several parts of the world. It is often brown in colour due to the presence of impurities.
$(c)$ When electricity is passed through an aqueous solution of sodium chloride (brine),it decomposes to form sodium hydroxide,chlorine gas,and hydrogen gas. This process is known as the chlor-alkali process. The chemical equation is: $2NaCl(aq) + 2H_2O(l) \xrightarrow{\text{Electricity}} 2NaOH(aq) + Cl_2(g) + H_2(g)$.

(N/A) Tooth decay starts when the $pH$ of the mouth falls below $5.5$. This occurs when bacteria present in the mouth produce acids by degrading sugar and food particles remaining in the mouth after eating. Using toothpaste,which is generally basic,helps neutralize the excess acid and prevents tooth decay.
$(b)$ If the $pH$ of a salt solution is greater than $7$,the nature of the salt is basic.
$(i)$ For Potassium sulphate $(K_2SO_4)$: Base is $KOH$ (Potassium hydroxide) and Acid is $H_2SO_4$ (Sulphuric acid).
$(ii)$ For Ammonium chloride $(NH_4Cl)$: Base is $NH_4OH$ (Ammonium hydroxide) and Acid is $HCl$ (Hydrochloric acid).

(N/A) Reactant: $CaSO_4 \cdot 2H_2O$ is known as Gypsum.
Product: $CaSO_4 \cdot \frac{1}{2}H_2O$ is known as Plaster of Paris $(POP)$.
Use: It is widely used by doctors as plaster for supporting fractured bones in the right position or for making toys,materials for decoration,and surfaces for smooth finishing.

(N/A) The nature of a salt depends on the strength of the acid and base from which it is formed. $A$ salt of a strong base and a weak acid is basic,while a salt of a strong acid and a weak base is acidic.

Salt	Acid	Base	Nature
$(i)$ Sodium acetate	Acetic acid $(CH_3COOH)$	Sodium hydroxide $(NaOH)$	Basic
$(ii)$ Ammonium sulphate	Sulphuric acid $(H_2SO_4)$	Ammonium hydroxide $(NH_4OH)$	Acidic

$A$ salt is formed by the neutralization reaction between an acid and a base. The cation of the salt comes from the base,and the anion comes from the acid.

Salt	Acid and Base
$(i)$ $Na_{2}SO_{4}$	Acid: $H_{2}SO_{4}$,Base: $NaOH$
$(ii)$ $NH_{4}Cl$	Acid: $HCl$,Base: $NH_{4}OH$
$(iii)$ $KNO_{3}$	Acid: $HNO_{3}$,Base: $KOH$
$(iv)$ $NaCl$	Acid: $HCl$,Base: $NaOH$

(B) The salt $NH_4Cl$ has a $pH$ less than $7$.
This is because $NH_4Cl$ is a salt formed from a strong acid $(HCl)$ and a weak base $(NH_4OH)$.
Strong acids ionize completely in water,while weak bases do not ionize completely.
Consequently,the resulting solution becomes acidic due to the presence of excess hydrogen ions $(H^+)$,leading to a $pH$ value of less than $7$.

(A) Compound $'A'$ is sodium carbonate $(Na_{2}CO_{3})$ and the gas evolved is carbon dioxide $(CO_{2})$.
The chemical reaction is as follows:
$Na_{2}CO_{3}(s) + H_{2}SO_{4}(aq) \to Na_{2}SO_{4}(aq) + CO_{2}(g) + H_{2}O(l)$
In this reaction,sodium carbonate reacts with dilute sulphuric acid to form sodium sulphate,water,and carbon dioxide gas. Carbon dioxide does not support combustion,which is why it extinguishes a burning candle.

(A) $(i)$ The lower the $pH$ of the solution,the higher the hydrogen ion concentration. Thus,solution $A$ $(pH = 6)$ has a higher hydrogen ion concentration compared to solution $B$ $(pH = 8)$.
$(ii)$ Solution $A$ is acidic because its $pH < 7$,while solution $B$ is basic because its $pH > 7$.

(N/A) An aqueous solution of sodium chloride $(NaCl)$ is neutral because it is a salt formed from the neutralization reaction between a strong acid $(HCl)$ and a strong base $(NaOH)$. Since both components are strong,the resulting salt solution does not undergo hydrolysis to change the $pH$ of the water,remaining at $pH = 7$.
An aqueous solution of sodium $(Na)$ is basic because sodium is a highly reactive alkali metal. When it reacts with water,it produces sodium hydroxide $(NaOH)$,which is a strong base,and hydrogen gas $(H_2)$. The presence of $NaOH$ in the solution increases the concentration of hydroxide ions $(OH^-)$,making the solution basic.
The chemical reaction is: $2Na(s) + 2H_2O(l) \longrightarrow 2NaOH(aq) + H_2(g)$

(N/A) Baking soda is basic in nature,so it neutralizes the acidic effect of the formic acid injected by an ant sting.
$(b)$ Baking soda $(NaHCO_{3})$ reacts with tartaric acid present in baking powder upon heating or mixing with water to release $CO_{2}$ gas. This $CO_{2}$ gas gets trapped in the dough,making the bread or cake soft and spongy.
$(c)$ Baking soda reacts with an acid (like $H_{2}SO_{4}$) to produce a large volume of $CO_{2}$ gas,which cuts off the oxygen supply and extinguishes the fire.

(N/A) Strong electrolytes are substances that dissociate completely into ions when dissolved in an aqueous solution. They conduct electricity very well due to the high concentration of ions. Examples: $NaCl$ (Sodium chloride) and $HCl$ (Hydrochloric acid).
Weak electrolytes are substances that dissociate only partially into ions in an aqueous solution. They conduct electricity poorly because only a small fraction of the molecules exist as ions. Examples: $CH_{3}COOH$ (Acetic acid) and $NH_{4}OH$ (Ammonium hydroxide).

(B) Curry contains turmeric,which acts as a natural acid-base indicator.
Soap is basic in nature.
When soap is applied to the turmeric stain,the basic medium causes the turmeric to turn reddish-brown.
When the cloth is washed with plenty of water,the soap is rinsed away,removing the basic medium.
As the medium is no longer basic,the turmeric returns to its original yellow color.

(N/A) When an acid reacts with a metal,$Hydrogen$ gas is liberated.
Example: When $Zinc$ granules react with dilute $Hydrochloric$ acid $(HCl)$,$Zinc$ chloride $(ZnCl_{2})$ and $Hydrogen$ gas $(H_{2})$ are produced.
$Zn(s) + 2HCl(aq) \longrightarrow ZnCl_{2}(aq) + H_{2}(g)$
Test for $Hydrogen$ gas: Bring a burning candle or a matchstick near the mouth of the test tube containing the gas. The gas burns with a characteristic '$pop$' sound,which confirms the presence of $Hydrogen$ gas.

(N/A) The chemical formula of bleaching powder is $CaOCl_{2}$.
Bleaching powder is prepared by the action of chlorine gas on dry slaked lime $[Ca(OH)_{2}]$. The chemical equation for the reaction is:
$Ca(OH)_{2} + Cl_{2} \longrightarrow CaOCl_{2} + H_{2}O$
In drinking water,it is used as a disinfectant to kill germs and bacteria,making the water safe for consumption.

(N/A) Dilute hydrochloric acid reacts with magnesium to form magnesium chloride and hydrogen gas is liberated.
$Mg(s) + 2HCl(aq) \longrightarrow MgCl_2(aq) + H_2(g)$
$(b)$ The reaction between dilute hydrochloric acid and sodium hydroxide is a neutralization reaction,forming sodium chloride salt and water.
$NaOH(aq) + HCl(aq) \longrightarrow NaCl(aq) + H_2O(l)$
$(c)$ Egg shells are primarily composed of calcium carbonate $(CaCO_3)$. Dilute hydrochloric acid reacts with calcium carbonate to produce calcium chloride,carbon dioxide gas,and water.
$CaCO_3(s) + 2HCl(aq) \longrightarrow CaCl_2(aq) + CO_2(g) + H_2O(l)$

(N/A) The substance $'X'$ is lime water,which is calcium hydroxide $\left[ Ca(OH)_{2} \right]$.
The chemical equation for the reaction of lime water with carbon dioxide is:
$Ca(OH)_{2}(aq) + CO_{2}(g) \longrightarrow CaCO_{3}(s) + H_{2}O(l)$
$(b)$ $'X'$ (calcium hydroxide) is obtained by the reaction of quick lime (calcium oxide) with water (slaking of lime).
The chemical equation is:
$CaO(s) + H_{2}O(l) \longrightarrow Ca(OH)_{2}(aq)$

(N/A) Tap water contains various dissolved salts that dissociate into ions when electricity is passed through it. These ions act as charge carriers,allowing the flow of electricity. In contrast,distilled water is pure and does not contain any dissolved salts or ions,making it an insulator that does not conduct electricity.

(N/A) Dry hydrogen chloride gas does not contain $H^{+}$ ions. Acids exhibit acidic properties only in the presence of water because they dissociate to produce hydrogen ions $H^{+}(aq)$. Since dry $HCl$ gas lacks water,it cannot release $H^{+}$ ions,and therefore,it does not show acidic behavior or change the color of blue litmus paper.

(N/A) $(i)$ The process of diluting a concentrated acid is a highly exothermic reaction. If water is added to a concentrated acid,the large amount of heat generated can cause the mixture to splash out,potentially leading to severe acid burns.
$(ii)$ Compounds like alcohol and glucose contain hydrogen,but they do not dissociate to release hydrogen ions $(H^+)$ when dissolved in water. Since acidic behavior is defined by the presence of $H^+$ ions in an aqueous solution,these compounds do not exhibit acidic properties.

(N/A) $(i)$ Plaster of Paris is written as $CaSO_{4} \cdot 1/2 H_{2}O$ because two formula units of $CaSO_{4}$ share one molecule of water of crystallization. This means that one water molecule is associated with two $CaSO_{4}$ units,effectively resulting in $1/2 H_{2}O$ per unit.
$(ii)$ Sodium hydrogen carbonate $(NaHCO_{3})$ is a mild,non-corrosive basic salt. It acts as an antacid by neutralizing the excess hydrochloric acid $(HCl)$ produced in the stomach,thereby providing relief from acidity.
$(iii)$ The electrolysis of an aqueous solution of sodium chloride (brine) produces chlorine gas $(Cl_{2})$ at the anode and sodium hydroxide $(NaOH)$,which is an alkali,at the cathode. Due to the formation of these two specific products,the process is termed the chlor-alkali process.

(D) The $pH$ value is defined as the negative logarithm of the hydrogen ion concentration,represented by the formula: $pH = -\log[H^+]$.
As the concentration of hydrogen ions $[H^+]$ increases,the value of $\log[H^+]$ also increases.
Since the $pH$ is the negative of this value,an increase in $[H^+]$ leads to a decrease in the $pH$ value.
Therefore,a higher concentration of hydrogen ions indicates a more acidic solution,which corresponds to a lower $pH$ value.

(A) The $pH$ scale is used to measure the acidity or alkalinity of a solution.
- $A$ $pH$ value of $1$ indicates a strong acid,which turns the $pH$ paper red.
- $A$ $pH$ value of $7$ indicates a neutral solution,which turns the $pH$ paper green.
- $A$ $pH$ value of $14$ indicates a strong base,which turns the $pH$ paper blue.
Therefore,the colours corresponding to $pH$ values $1, 7,$ and $14$ are red,green,and blue,respectively.

(B) strong acid is an acid that completely dissociates into its ions in an aqueous solution.
$H_2SO_4$ (Sulphuric acid) is a mineral acid and is considered a strong acid because it ionizes completely in water.
Ethanoic acid $(CH_3COOH)$,Tartaric acid,and Citric acid are organic acids,which are generally weak acids as they only partially dissociate in water.

(C) weak acid is an acid that partially dissociates into its ions in an aqueous solution.
$H_2SO_4$ (Sulphuric acid),$HNO_3$ (Nitric acid),and $HCl$ (Hydrochloric acid) are strong acids because they dissociate completely in water.
$CH_3COOH$ (Ethanoic acid or Acetic acid) is a weak acid because it only partially dissociates in water,resulting in a lower concentration of $H^+$ ions.

(D) Mineral acids are acids derived from inorganic compounds,typically non-living sources.
Citric acid,Lactic acid,and Oxalic acid are organic acids found in plants and animals.
Nitric acid $(HNO_3)$ is a mineral acid prepared from inorganic minerals.
Therefore,the correct option is $D$.

(A) Oxalic acid is a dicarboxylic acid found in various plants.
Among the given options,tomato contains oxalic acid.
Orange contains citric acid,sour milk contains lactic acid,and tamarind contains tartaric acid.

(B) The chemical compound used in glass, soap, and paper industries is sodium carbonate, commonly known as washing soda $(Na_2CO_3 \cdot 10H_2O)$.
It is widely used in the glass, soap, and paper industries because it acts as a strong base and a cleaning agent.
Baking soda $(NaHCO_3)$ is primarily used for cooking and as an antacid.
Lime water $(Ca(OH)_2)$ is used in the laboratory and for whitewashing.
Bleaching powder $(CaOCl_2)$ is used for disinfecting water and bleaching fabrics.

(C) Gypsum is a naturally occurring mineral with the chemical formula $CaSO_4 \cdot 2H_2O$ (calcium sulfate dihydrate).
Plaster of Paris is produced by heating gypsum at $373 \ K$ $(100^{\circ}C)$,which causes it to lose water molecules and become calcium sulfate hemihydrate,with the formula $CaSO_4 \cdot \frac{1}{2}H_2O$.

(D) Bleaching powder,chemically known as calcium oxychloride $(CaOCl_2)$,is widely used as an oxidising agent in many chemical industries.
It acts as a strong oxidising agent because it releases nascent oxygen when it reacts with water or dilute acids.
This property makes it useful for bleaching cotton and linen in the textile industry,bleaching wood pulp in paper factories,and for disinfecting drinking water.

(C) Permanent hardness of water is caused by the presence of dissolved chlorides and sulfates of calcium and magnesium.
Sodium carbonate $(Na_{2}CO_{3})$,commonly known as washing soda,is used to remove this permanent hardness.
It reacts with the calcium and magnesium ions to form insoluble carbonates,which can then be filtered out.
The chemical reaction is: $Ca^{2+} + CO_{3}^{2-} \rightarrow CaCO_{3} \downarrow$ and $Mg^{2+} + CO_{3}^{2-} \rightarrow MgCO_{3} \downarrow$.
Therefore,$Na_{2}CO_{3}$ is the correct compound.

(B) Common salt $(NaCl)$ is a crucial raw material for various chemicals used in daily life and industry.
$1$. Washing soda $(Na_2CO_3 \cdot 10H_2O)$ is produced from $NaCl$ via the Solvay process.
$2$. Bleaching powder $(CaOCl_2)$ is produced by the action of chlorine gas (obtained from the electrolysis of brine, i.e., $NaCl$ solution) on dry slaked lime.
$3$. Baking soda $(NaHCO_3)$ is produced using $NaCl, NH_3, CO_2,$ and $H_2O$.
Slaked lime $(Ca(OH)_2)$ is produced by adding water to quicklime $(CaO)$, not from common salt.
Therefore, $(i), (ii),$ and $(iii)$ are correct.