Dyes and Pigment Questions in English

(B) Lithopone is a mixture of $ZnS$ and $BaSO_4$. It is used as a white pigment,not a yellow pigment. Therefore,the statement in option $(B)$ is incorrect.

(D) Lithopone is a mixture of zinc sulfide $(ZnS)$ and barium sulfate $(BaSO_4)$.
It is widely used as a white pigment in paints and coatings.

(D) Molybdenum compounds,such as molybdenum trioxide $(MoO_3)$ and various molybdates,are widely used in industrial applications.
They are used as pigments in the dye industry,for colouring leather,and for colouring rubber.
Therefore,all the given options are correct.

(D) Chrome green is a pigment composed of $Cr_2O_3$ (Chromium$(III)$ oxide). It is a stable,green-colored compound used extensively in paints and ceramics.

(C) Diazo-coupling reactions involve the reaction of a diazonium salt with an aromatic compound (like phenols or amines) to form azo compounds.
These azo compounds are characterized by the $-N=N-$ linkage and are extensively used as synthetic dyes due to their intense colors.
For example,the reaction of benzene diazonium chloride with aniline produces $p$-aminoazobenzene,which is a yellow dye.

(C) The correct answer is $C$.
Magenta is a triphenylmethane dye,specifically $p-$rosaniline hydrochloride.
It is commonly used in the Schiff's test for the identification of aldehydes.

(C) $Indigo$ dye is a vat dye with the chemical formula $C_{16}H_{10}N_2O_2$. Its structure consists of two indole units joined by a central double bond. Option $C$ correctly represents the structure of $Indigo$.

(C) Developed dyes,also known as ingrain dyes,are those which are synthesized directly on the fabric.
For example,azo dyes are formed on the fabric by coupling reactions.
Ingrain dyeing is particularly suitable for cotton fabric.

(D) $Eosin$ is a fluorescent acidic compound which is used as a red dye in the preparation of red ink.

(C) The blueprint process is a reproduction technique that uses a light-sensitive iron compound,specifically $ferric \ ammonium \ citrate$ and $potassium \ ferricyanide$.
When exposed to light,the iron$(III)$ is reduced to iron$(II)$,which then reacts with the ferricyanide to form an insoluble blue pigment known as $Turnbull's \ blue$ $(Fe_3[Fe(CN)_6]_2)$.
Therefore,the correct answer is $C$.

(A) The correct answer is $(A)$.
This is a coupling reaction in which an aromatic diazonium salt (e.g.,$C_6H_5N_2Cl$) reacts with a phenol or an aromatic amine to form an azo compound,which acts as a dye.
The reaction is:
$C_6H_5N_2Cl + C_6H_5OH \rightarrow C_6H_5-N=N-C_6H_4OH + HCl$
(Benzene diazonium chloride + Phenol $\rightarrow$ $p$-hydroxyazobenzene).

(B) mordant is any substance which can be fixed to the fibre and which can be dyed later on. Mostly hydroxide or basic salts of chromium,aluminium,and iron are used as mordant.
$A$ dye which imparts different colours in the presence of different mordants is referred to as a mordant dye.
For example,alizarin is a mordant dye when mordanted with aluminium salt solution. It imparts rose red colour to fabric,but the same fabric is dyed blue when it is mordanted with barium salt and it dyes violet if mordanted with ferric salt.

(A) The insoluble coloured compound formed by the reaction of metallic salts with dyes is known as a $Lake$.
These are often used in pigments and printing inks.

(A) The correct answer is $(A)$.
Alizarin is a naturally occurring mordant dye.
Chemically,it is identified as $1, 2-$dihydroxy anthraquinone.
The structure consists of an anthraquinone core with hydroxyl groups attached at the $1$ and $2$ positions.

(D) $ (d) $ Phenolphthalein belongs to the class of phthalein dyes because it is synthesized from the condensation of phthalic anhydride with phenol.

(C) Alizarin is a classic example of a mordant dye,which requires a metal salt (mordant) to fix the dye onto the fabric. It is extensively used in cotton dyeing,printing,and the preparation of chromium lakes for wood dyeing. It is not used in painting because it lacks the necessary affinity for the binders used in paints and requires a mordant to develop its color.

(D) dye is a colored substance that has an affinity to the substrate to which it is being applied.
Methyl orange,Orange $I$,and Aniline yellow are all synthetic azo dyes used for coloring various materials.
Therefore,all of the given options are examples of dyes.

(B) Basic dyes contain $-NH_2$ or $-NR_2$ groups as colour-bearing or colour-enhancing groups.
They are generally used for dyeing wool,cotton,leather,paper,polyester,nylon,etc.
Examples include aniline yellow,crysodine $G$,butter yellow,and malachite green.

(B) Direct dyes adhere to the fibre through hydrogen bonding.
They belong to the class of azo dyes.
They are used to dye the fabric directly by placing it in a hot aqueous solution of the dye.
For example: Martius yellow,Congo red,etc.

(A) Vat dyes are insoluble compounds which upon reduction give a soluble (leuco) form.
This leuco form has an affinity for specific fabrics and is absorbed by the fiber.
Upon oxidation,the dye is regenerated in its insoluble form within the fiber.
$Indigo$ is a classic example of a vat dye commonly used for dyeing denim jeans.

(A) mordant is a substance used to set or fix dyes on fabrics or tissue sections by forming a coordination complex with the dye,which then attaches to the fabric or tissue.
It is commonly used in the dyeing process to ensure the color binds effectively to the fibers.

(C) is the correct answer.
Disperse dyes are usually applied in the form of a dispersion of finely divided dye in a soap solution in the presence of Phenol,Cresol,Benzoic acid,etc.
They are mainly used to dye synthetic fibers like Dacron and nylon.
Example: $Celliton$ (blue).

(A) Malachite green is prepared by the condensation of $1$ mole of benzaldehyde with $2$ moles of $N,N$-dimethylaniline in the presence of an acid catalyst,followed by oxidation.

(B) Fluorescein is a synthetic dye prepared by the condensation reaction of $1$ mole of phthalic anhydride with $2$ moles of resorcinol in the presence of a dehydrating agent like concentrated $H_2SO_4$ or $ZnCl_2$.

(C) is the wrong statement. Indigo is a dark blue solid that is insoluble in water. It must be reduced to its soluble leuco-form to be used in the vat dyeing process.

(NONE) The correct chemical name of alizarin is $1, 2-$dihydroxyanthraquinone. However,the statement in option $B$ is often considered technically incomplete or incorrect in some contexts because the structure of alizarin is $1, 2-$dihydroxyanthraquinone,but it is specifically a derivative of anthraquinone. Upon reviewing the options,all statements $A$,$C$,and $D$ are factually correct regarding the properties and historical use of alizarin. Since the question asks for the wrong statement and all provided options are chemically accurate descriptions of alizarin,there is no 'wrong' statement among the choices provided. In many competitive exam contexts,if forced to choose,one might scrutinize the naming convention,but chemically,all are correct.

(C) The colour observed is the complementary colour of the light absorbed by the substance.
Since the dye appears red,it absorbs the complementary colour,which is green.
Therefore,the correct option is $(C)$.

(A) $Alizarin$ is a well-known example of an anthraquinone dye,which is derived from the anthraquinone structure.

(B) Aniline yellow is a basic dye.
Basic dyes are synthetic dyes that act as bases and are typically used for dyeing wool,silk,and acrylic fibers.
Therefore,the correct option is $(B)$.

(A) . Vat dyes are insoluble compounds which,upon reduction,yield a soluble leuco form. This leuco form has an affinity for specific fabrics and is subsequently oxidized back to the insoluble coloured state on the fabric. $A$ classic example is $Indigo$.

(D) Benzene is a known carcinogen and is not used as a solvent in nail polish. Nail polish typically contains cellulose nitrate as a film-forming agent,acetone as a solvent,and various dyes for color.

(D) The correct answer is $(D)$. Acid dyes are characterized by the presence of acidic functional groups such as $-COOH$,$-SO_3H$,or phenolic groups.
These dyes are typically applied in an acidic medium and show affinity for protein fibers like wool,silk,and nylon.
Methyl orange,Methyl red,and Phenolphthalein all possess acidic functional groups that allow them to act as acid-base indicators and function as acidic dyes in specific applications.

(C) Alizarin is a typical mordant dye that gives different colours depending on the metal ion used as a mordant.
When alizarin is mordanted with $Al^{3+}$ ions,it forms a coordination complex that produces a rose-red colour.
Therefore,the metal ion involved is $Al^{3+}$.

(A) Azo dyes are prepared from aniline.
First,aniline $(C_6H_5NH_2)$ reacts with $NaNO_2$ and $HCl$ at $273-278 \ K$ to form benzene diazonium chloride $(C_6H_5N_2^+Cl^-)$.
This benzene diazonium chloride then undergoes a coupling reaction with phenols or aromatic amines to produce azo dyes,which are characterized by the $-N=N-$ linkage.

(D) Nylon and polyester are synthetic fibers that are hydrophobic in nature.
Disperse dyes are commonly used for these fibers because they are finely divided and can penetrate the fiber structure.
Basic dyes are also used for acrylic fibers.
However,$Vat$ dyes and $Insoluble$ dyes are generally not used for dyeing synthetic fibers like nylon and polyester because they are designed for cellulosic fibers like cotton.
Among the given options,$Vat$ dyes are specifically known for their application on cotton and are not suitable for synthetic fibers.

(A) $2, 4, 6-$Trinitrophenol is commonly known as picric acid.
It is an acidic compound containing three nitro groups $(-NO_2)$ which are strongly electron-withdrawing,making the phenolic $-OH$ group highly acidic.
Due to its acidic nature and ability to impart color to protein fibers (like wool and silk),it is classified as an acidic dye.

(B) Diazonium salts are highly reactive intermediates that are widely used in organic synthesis,particularly for the preparation of various azo dyes. Through coupling reactions with phenols or aromatic amines,they form stable,colored compounds known as azo dyes.

(A) An azo dye is a compound containing the azo group,$-N=N-$,linked to aromatic rings.
Methyl orange is a well-known azo dye used as an acid-base indicator.
Its chemical structure contains the $-N=N-$ linkage,which is characteristic of azo dyes.

(D) An auxochrome is a group of atoms which,when attached to a chromophore,modifies the ability of the chromophore to absorb light,often shifting the absorption to longer wavelengths.
Groups like $-N(CH_3)_2$,$-OH$,and $-OCH_3$ contain lone pairs of electrons and act as auxochromes.
The group $>C=N-$ is a chromophore,not an auxochrome.

(A) Indigo is a naturally occurring organic compound that acts as a blue dye. It is historically significant and is classified as an organic dye.

(A) Orange-$I$ is an acid azo dye. It is prepared by the coupling reaction of diazotized sulfanilic acid with $\alpha$-naphthol.

(C) Basic dyes are synthetic dyes that contain basic groups like $-NH_2$ or $-NHR$ in their structure.
$Methylene \ blue$ is a well-known cationic (basic) dye used in biological staining and textile dyeing.
$Congo \ red$ is an acidic dye,while $Aniline \ yellow$ is a solvent dye and $Phenolphthalein$ is an acid-base indicator.

(D) chromophore is a group of atoms in a molecule that is responsible for its color. Common examples of chromophores include $-N=N-$ (azo group),$-NO$ (nitroso group),and $-NO_2$ (nitro group). The $-NH_2$ (amino group) is an auxochrome,which is a group that modifies the ability of a chromophore to absorb light but does not produce color on its own. Therefore,$-NH_2$ is not a chromophore.

(A) Vat dyes are water-insoluble dyes that are applied to fabrics in a reduced,soluble form and then oxidized back to the insoluble state within the fiber. $Indigo$ is a classic example of a vat dye.

(B) Dyes are synthetic organic compounds that are used to impart color to fabrics and other materials. Historically and industrially,most synthetic dyes are derived from aromatic hydrocarbons,which are primarily obtained from $Coal \ tar$.

(A) When resorcinol reacts with phthalic anhydride in the presence of concentrated $H_2SO_4$,a condensation reaction occurs to form fluorescein. Fluorescein is a well-known fluorescent dye. Therefore,the product formed is a dye.

(B) Dyes are natural or synthetic chemical substances used to impart color to fabrics,plastics,paper,etc.,including food items for their pleasant appearance.
Alizarin (orange-red) is a natural dye extracted from the root of the madder plant,although it is also synthesized today.

(C) The correct answer is $(C)$.
Indigo is a natural dye obtained from the plant $Indigofera \text{ } tinctoria$,which was historically cultivated on a large scale in India.

(B) $Indigo$ belongs to the class of $Vat$ dyes.
$Vat$ dyes are insoluble in water and must be reduced to a soluble form (often called the $Leuco$ form) in an alkaline medium to be applied to the fabric.
Upon oxidation (usually by exposure to air),the $Leuco$ form is converted back into the insoluble,colored pigment within the fiber,ensuring excellent wash fastness.

(A) Lithopone is a white pigment that is a mixture of zinc sulfide $(ZnS)$ and barium sulfate $(BaSO_4)$.
It is prepared by the co-precipitation of these two compounds.
Therefore,the correct composition is $ZnS$ and $BaSO_4$.