(i) It is because of lower bond dissociation energy in the case of \({ R }^{ \_ \_ \_ }{ I }\) than \({ R }^{ \_ \_ \_ }{ Cl }\). \({ R }^{ \_ \_ \_ }{ Cl }\)  is more polar than  \({ R }^{ \_ \_ \_ }{ Br }\) , therefore, more reactive.
(ii) It is because it forms stable carbocation, therefore , follows S_N 1 mechanism.

(iii) Ethers are not associated with H-bonding and have weak van der Waal's forces of attraction, hence they have low boiling point.

DNA contains, Adenine, Thymine, Guanine and Cytosine.
Thymine is not present in RNA. Instead of Thymine RNA contains Uracil.

Aspirin gets hydrolysed to form salicylic acid which may damage cell walls whereas paracetamol does not harm the cell walls. Secondly, aspirin cannot be given to ulcer patients.

A 50 : 50 mixture of two enantiomers of any optically active compound is called a racemic mixture. It is always optically inactive since rotation caused by the molecules of one enantiomer. For example, an equimolar mixture of (+)-2 bromobutane and (-) -2- bromobutane is called a racemic mixture.

Pentan-2-one is a methyl ketone (i.e., contains the grouping CH₃CO) and hence undergoes Iodoform test on treatment with I₂/ NaOH to give yellow ppt. of iodoform. In contrast, pentan-3-one is not a methyl ketone and hence does not give yellow ppt. of CHI₃ on treatment with I₂/ NaOH.

(i)The ion whose one end is positively charged and other end is negatively charged is called Zwitter ion, e.g., 
\({ H }_{ 2 }N-CH_{ 2 }-COOH\rightleftharpoons { H }_{ 3 }^{ \oplus }N-CH_{ 2 }-COO^{ - }\)
(ii) Glycosidic Linkage: The oxide linkage between monosachharide units in oligo and polysachharide is called glycosidic linkage, e.g.

Antiseptics: These are chemicals which kill or prevent the growth of micro-organisms. They are applied to living tissues.
Disinfectants: They kill microorganisms but are not safe for contact with living tissues. 0.2% solution of phenol is antiseptic. 2% solution of phenol is disinfectant.

The following tests are used to distinguish between phenol and ethanol:
(i) Bromine water test. When phenol is treated with bromine water, it gives pale yellow precipitate of 2, 4, 6-tribromophenol.
Ethanol does not give this test.
(ii) FeCl₃ test. With FeCI₃, phenol gives characteristic purple, violet or red colouration while ethanol does not give any colour.

It is because even the traces of certain impurities, which can act as chain transfer agent (or inhibitor can interfere with the original polymerisation chain reaction. Hence, monomers should be free from all impurities, particularly inhibitors (or chain tranfer agents) like CC _4,CBr _4, amines, phenols, quinones etc _.

(i) Cyanohydrin:
Cyanohydrins are organic compounds having the formula RR“²C(OH)CN, where R and R“² can be alkyl or aryl groups.
 
Aldehydes and ketones react with hydrogen cyanide (HCN) in the presence of excess sodium cyanide (NaCN) as a catalyst to field cyanohydrin. These reactions are known as cyanohydrin reactions.
 
Cyanohydrins are useful synthetic intermediates.
 
When aldehydes are treated with two equivalents of a monohydric alcohol in the presence of dry HCl gas, hemiacetals are produced that further react with one more molecule of alcohol to yield acetal.
 
(iii) Semicarbarbazone:
Semicarbazones are derivatives of aldehydes and ketones produced by the condensation reaction between a ketone or aldehyde and semicarbazide. 

Semicarbazones are useful for identification and characterization of aldehydes and ketones. 

(iv) Aldol:
A Ã�²–hydroxy aldehyde or ketone is known as an aldol. It is produced by the condensation reaction of two molecules of the same or one molecule each of two different aldehydes or ketones in the presence of a base.
 
(v) Hemiacetal:
Hemiacetals are α - alkoxyalcohols
General structure of a hemiacetal
Aldehyde reacts with one molecule of a monohydric alcohol in the presence of dry HCl gas.

(vi) Oxime:
Oximes are a class of organic compounds having the general formula RR“²CNOH, where R is an organic side chain and R“² is either hydrogen or an organic side chain. If R“² is H, then it is known as aldoxime and if R“² is an organic side chain, it is known as ketoxime.

On treatment with hydroxylamine in a weakly acidic medium, aldehydes or ketones form oximes.

(vii) Ketal:
Ketals are gem - dialkoxyalkanes in which two alkoxy groups are present on the same carbon atom within the chain. The other two bonds of the carbon atom are connected to two alkyl groups.

Ketones react with ethylene glycol in the presence of dry HCl gas to give a cyclic product known as ethylene glycol ketals. 

(viii) Imine:
Imines are chemical compounds containing a carbon nitrogen double bond.

Imines are produced when aldehydes and ketones react with ammonia and its derivatives. 

(ix) 2, 4 - DNP - derivative:
2, 4 - dinitrophenylhydragones are 2, 4 - DNP - derivatives, which are produced when aldehydes or ketones react with 2, 4 - dinitrophenylhydrazine in a weakly acidic medium.

To identify and characterize aldehydes and ketones, 2, 4 - DNP derivatives are used.
(x) Schiff's base:
Schiff's base (or azomethine) is a chemical compound containing a carbon-nitrogen double bond with the nitrogen atom connected to an
aryl or alkyl group-but not hydrogen. They have the general formula R₁R₂C = NR₃. Hence, it is an imine.
It is named after a scientist, Hugo Schiff.

Aldehydes and ketones on treatment with primary aliphatic or aromatic amines in the presence of trace of an acid yields a Schiff's base.

(i) HOCI in presence of an acid generates the reactive electrophile, chloronium ion «r, which attacks benzene to give chlorobenzene (A).
(ii) Chlorobenzene (A) on treatment with NaNH2/liq. NH₃ undergaes-dehydrohalogenation via benzyne to afford aniline (B).
(iii) Aniline (B) on treatment with HBF4 forms the corresponding salt anilinium tetrafluoroborate (C) which on heating with NaNO₂ undergoes Balz-Schiemann reaction through the intermedium formation of benzenediazonium tetrafluoroborate to afford fluorobenzene (D).

(i) Since compound (A) with M.F. C₂H₄O reduces Tollens' reagent, it must be an aldehyde, i.e., acetaldehyde (CH₃HO).
\(\underset{Acetaldehyde}{CH_3CHO}+\underset{Tollens\ reagent}{2[Ag(NH_3)_2]^+}+3OH^-\longrightarrow CH_3COO^-+2Ag\downarrow+4NH_3+2H_2O\)
(ii) In presence of Al(OC₂H₅)₃ aldehydes undergo Tischenko reaction to give esters. Thus, when two moles of acetaldehyde (CH₃CHO) react in presence of AI(OC₂H₅)₃ ethyl acetate (B) with M.F. C₄H₈O₂ is produced
\(\underset{Acetaldehyde(A)\\(Two\ moles)}{CH_3CHO+OHCCH_3}\xrightarrow[(Tischenko reaction)]{Al(OC_2H_5)_3}\underset{Ethyl\ acetate\\ M/F.\ C_4H_8O_2}{CH_3COOCH_2CH_3}\)
(iii) The structure of ethyl acetate (B) is confirmed by the observation that on treatment with NH₃, it gives one molecule of an alcohol, i.e., ethyl alcohol, CH₃CH₂OH (C) and one molecule of an amide, i.e., acetamide, CH₃CONH₂(D)
\(\underset{Ethyl\ acetate(B)}{CH_3COOCH_2CH_3}\xrightarrow{NH_3}\underset{Ethyl alcohol (C)\\ M.F. C_2H_6O}{CH_3CH_2OH}+\underset{Acetamide (D)\\ M.F. C_2H_5NO}{CH_3CONH_2}\)

(i) Since compound (A) on treatment with CHCI3 and KOH (i.e., Reimer-Tiemann reaction), gives two products Band C, therefore, A must be phenol and Band C must be o-hydroxybenzaldehyde and P: hydroxybenzaldehyde respectively or vice-versa.
(ii) Since both Band C on distillation with Zn dust give the same compound (D), therefore, D must be benzaldehyde.
(iii) Since oxidation of D gives E with M.F. C7R602, therefore, E must be benzoic acid.
(iv) Since sodium salt of E, i.e.benzoic acid upon heating with soda-lime gives compound (F), therefore.
(F) must be benzene. Zn dust distillation of A would also give benzene (F).

During osazone formation, the reaction occurs only at CI and C2 while rest of the molecule remains intact. Since glucose and fructose differ from each other only in the arrangement of atoms at CI and C2, therefore, they. give the same osazone.

(i) Chemical name of the poisonous vapours is methyl isocynate(MIC)
(ii) It can be prepared by heating methyl amine and phosgene.
(iii) The compound is highly reactive towards group like hydroxyl,amino, thio etc  which are present in enzymes , proteins , carbohydrates , cellular fluids like water present in human system. It destroys the lung tissues and causes acute breathing problems It is also absorbed by the skin and causes its destruction.
(iv) The factories where such chemicals are produced must be installed away from the cities and villages, preferably in remote areas. Proper training must be given to the factories and inspections must be carried out from time to time to ensure that everything is in order.

N-Methylebenzylamine (CH₃NHCH₂C₆H₅) being a \({ 2 }^{ \circ }\) amine cannot be prepared by Gabriel's synthesis.