Baking soda ($NaHCO_3$) does not contain water of crystallization. Others like washing soda ($Na_2CO_3 · 10H_2O$), gypsum ($CaSO_4 · 2H_2O$), and blue vitriol ($CuSO_4 · 5H_2O$) contain water molecules.

Vinegar contains acetic acid ($CH_3COOH$), not benzoic acid, so statement 3 is false. Statements 1, 2, and 4 are true.

The substance that turns blue litmus red is acidic, which has a pH value less than 7. The value 5 given in option (D) is less than 7, hence it is acidic.

Correct match:
A. Citric acid - 2. Lemon
B. Butyric acid - 1. Butter
C. Acetic acid - 4. Vinegar
D. Lactic acid - 3. Milk
Thus, the correct code is 2-1-4-3.

When an acid reacts with a metal, hydrogen gas is evolved and a corresponding salt is formed.

Magnesium hydroxide [$Mg(OH)_2$] is a base, its nature is basic.

The neutral color of phenolphthalein is colorless. Phenolphthalein indicator remains colorless in acidic solution. Phenolphthalein indicator produces pink color in alkaline solution.

According to the Bronsted-Lowry theory, a substance that donates a proton ($H^+$) is called an acid.

When the sodium lamp is lit, it emits a light red/pink light, and after a few moments when the sodium gets hot, it starts emitting a bright yellow color because the sodium metal vaporizes. (Note: This is as per the explanation provided in the book).

In Aqua regia, the ratio of $HCl$ to $HNO_3$ is 3:1. The question asks for the ratio of $HNO_3$ to $HCl$ respectively, so it will be 1:3.

Acidic Salt: A general salt that is formed by the neutralization of a strong acid and a weak base is called an acidic salt. Example- Ammonium chloride ($NH_4Cl$)

Litmus is a natural indicator, which is obtained from Lichens.

$C_2H_5OH$ is not a base, it is an alcohol. Its chemical name is ethanol or ethyl alcohol.

In nitrophenol, the $-NO_2$ group is electron-withdrawing, which increases acidity, while the $-CH_3$ (methyl) group is electron-donating, which decreases acidity. Thus the order will be I > II > III.

In the year 1909, a scientist named S.P.L. Sorensen created the pH scale.

The reactions in which acid and base react to form water and salt are called neutralization reactions in chemistry. It is also called elimination reaction.

$NH_4OH (Ammonium hydroxide) + HCl (Hydrochloric acid) \rightarrow NH_4Cl (Ammonium chloride) + H_2O$. Ammonium chloride is released as white smoke.

In an alkaline medium, the oxidation state of Mn in $MnO_4^-$ changes from +7 to +4 ($MnO_2$), the change is 3, so the equivalent weight will be $M/3$.

In the chlor-alkali process, the aqueous solution of sodium chloride (brine) is electrolyzed, which produces sodium hydroxide ($NaOH$), chlorine gas, and hydrogen gas.

According to the question, pH = 5.2. We know that $pH + P_{OH} = 14$. Therefore, $P_{OH} = 14 - 5.2 = 8.8$.