Formic acid(Methanoic acid) HCOOH.

(a) According to Arrhenius theory, acids are substances that produce H⁺ ions when mixed with water.  On the other hand, based are substances that produce OH^- ions when mixed with water.
(b) NH₄OH is a weak base and HCl is a strong acid.

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.

Red litmus turns blue in solution of ammonium hydroxide.

Curd and sour substances contain acids which react with copper and brass to form certain salts that are poisonous in nature and can cause food poisoning. Hence, sour substances like curd, pickles etc., should not be kept in brass and copper vessels.

(a) Concentrated sulphuric acid is called the king of chemicals as it is a very strong acid and is highly corrosive.

(b) The three chemical reactions that take place during the conversion of sulfur dioxide to sulphuric acid in the 'Contact Process' are given below.

Step I: Sulphur dioxide is mixed with air and passed over vanadiumpent (V) oxide catalyst heated to \(450^oC\) to form sulphur trioxide.

\(\underset{Sulphur\ dioxide}{2SO_{2(g)}}+\underset{Oxygen}{O_{2(g)}}\underset{\rightleftharpoons }{V_2O_5}\underset{Sulphur\ trioxide}{2SO_{3(g)}}+Heat\)

Step II : Sulphur trioxide is dissolved in concentrated sulphuric acid to form a thick fuming liquid called oleum.

\(\underset{Sulphuric\ acid}{H_2SO_4(l)}+\underset{Sulphur\ trioxide}{SO_{3(g)}}\begin{matrix} V_2O_5 \\ \rightleftharpoons \\ \end{matrix}\underset{Oleum}{H_2S_2O_{7(l)}}\)

Step III: Oleum is diluted with a calculated quantity of water to obtain sulphuric acid.

\(H_2S_2O_{7(l)}+\underset{Water}{H_2O_{(l)}}\rightarrow\underset{Sulphuric\ acid}{2H_2SO_{4(aq)}}\)

(c) If water is added to sulphuric acid then a large amount of heat is evolved.  This changes water to steam, which can splash the acid.  Hence, it is dangerous.

The gas evolved at anode during electrolysis of brine is chlorine (G) When chlorine gas is passed through dry \(Ca(OH)_2\ (Y)\) produces bleaching powder (Z) used for disinfecting drinking water.
\(Ca(OH)_2+Cl_2\rightarrow CaOCl_2+H_2O\)
Since Y and Z are calcium salts, therefore X is also a calcium salt and is calcium carbonate.
\(CaCO_3+2HCl\rightarrow CaCl_2+CO_2+H_2O\)
\(Ca(OH)_2+CO_2 \rightarrow CaCO_3+H_2O\)

Hydrogen gas is usually liberated when an acid reacts with metal.
e.g. Zn(s) + H₂SO₄ (aq) \(\rightarrow\) ZnSO₄(aq) + H₂ \(\uparrow\)
Test for H₂ gas Testing of H₂ gas presence can be done by passing the gas through soap solution and then bringing a burning splinter near the soap bubble filled with the gas. If the gas burns with a pop sound, it confirms hydrogen.

(i) Increase in the strength of alkali. So the nature of solution will be basic.
(ii) Hydroxide ion or hydroxyl ion or OH^- ion.
(iii) A paper impregnated with the universal indicator is generally used to measure the pH of a solution.

(i) Tomato - Malic acid and citric acid
(ii) Vinegar - Acetic acid
(iii) Tamarind - Tartaric acid and citric acid.