1 M HCl has a higher concentration of H⁺  ions because when HCl dissolves in water it dissociates completely into ions while CH₃COOH is a weak acid and does not dissociate into ions completely.

X - NaOH (Sodium hydroxide)
A - Na₂ZnO₂ (Sodium zincate)
B - NaCI (Sodium chloride)
C - CH₃COONa (Sodium acetate)

A represents an acid solution.  This is because the pH value of A is 2.0 and the pH value of an acids lies between 1 and 6.

When the pH in mouth is lower than 5.5, it means acids are formed due to food decay by bacteria in our mouth.  The acid released will react with enamel.  As the enamel is made up of calcium phosphate, tooth decay starts.

When fresh milk turns into curd, its pH value will decrease.  This is because lactic acid is produced when decrease.  This is because lactic acid is produced when milk changes into curd.

When crystals of washing soda are left open in dry air, they lose nine water molecules to form sodium carbonate monohydrate.

\(Na_2CO_3.10H_2O\rightarrow Na_2CO_3.H_2O+9H_2O\)

Washing soda is used industrially as cleansing agent in laundry.  Also, it used for softening hard water in industries.

The chemical formula of baking powder is sodium hydrogen carbonate \((NaHCO_3).\) while, that of washing soda is sodium carbonate carbonate on heating gives \(CO_2\) gas which will turn lime water milky whereas no such gas is obtained from sodium carbonate.

\(2NaHCO_3\xrightarrow {Heat}Na_2CO_3+H_2O+CO_2\)
\(NA_2CO_3.10H_2O\xrightarrow {Heat}Na_2CO_3+10H_2O\)

The student adds turmeric to the two beakers.  The basic solution turns the turmeric into reddish-brown in basic solution.  On the other hand, she added few drops of phenolphthalein solution to the beakers.  If a colourless substance is produced, the substance is acidic and if a pink colour is produced, the solution said to be basic.

Commonly used compounds for making chalks and other pottery articles is plaster of paris.  Its chemical formula is \((CaSO_4)_2.{1\over2}2H_2O\) onn partical losing water of crystallization by controlled heating of crystallization by controlled heating \(120^o-130^oC.\)  When \(CaSO_4.2H_2O\) is strongly heated it loses whole of water of crystallisation and gives anhydrous calcium sulphate.  Thus 'x' is \(CaSO_4.2H_2O\) is strongly heated it loses whole of water of crystallisation and gives anhydrous calcium sulphate.  Thus 'x' is \(CaSO_4.2H_2O;\) y is \(CaSO_4.{1\over2}H_2O\) and 'z' is \(CaSO_4.\)

\(2CaSO_4.2H_2O\xrightarrow{heat/120^o-130^o\ C}(CaSO_4)_2.{1\over2}H_2O+{3\over 2}H_2O(g)\)

\(2CaSO_4.2H_2O\xrightarrow{heat/>130^oC}CaSO_4\)

Hydrochloric acid gives white fumes of ammonium chloride when in contact with ammonia.  Thus, sodium chloride from sea water reacts with dilute \([H_2SO_4]\) to HCl gas. Dry HCl gas has no effect on litmus paper.

Plaster of Paris (POP) is chemically calcium sulphate hemihydrate (CaSO₄.\(\frac{1}{2}\)H₂O). When it comes in contact with water it sets into a hard solid mass, called gypsum.
CaSO₄. \(\frac{1}{2}\) H₂O + 1\(\frac{1}{2}\)H₂O \(\rightarrow\) CaSO₄ . 2H₂O
  Plaster of Paris                           Gypsum
To prevent this, POP must be stored in moisture-proof containers.

(i) Alkaline medium does not allow milk to turn sour easily.
(ii) When milk is set to curd, the presence of alkali does not allow it to become acidic easily. Hence, this milk take a longer time to set as a curd.

An acid dissociates into hydronium ions (H₃O⁺) and anions when dissolved in water. When a solution is diluted, the volume of the solution increases but the number of ions remains the same, so concentration of hydronium ions (H₃O⁺) per unit volume decreases.

Dry HCl gas does not contain any H⁺ or H₃O⁺ ions, so it does not show any acidic property. Hence, it does not change the colour of dry litmus paper. To show its acidic behaviour, it needs wet litmus paper.