Melibiose disaccharide is composed of one glucose monomer and one galactose monomer.

This is correct.

The Benzoin condensation is a coupling reaction between two aldehydes that allows the preparation of α-hydroxyketones in the presence of CN^- and alcohol. The reagents Na, C₂H₅OH, NH₃ are employed in Birch reduction to reduce conjugation.

A disaccharide is the carbohydrate formed when two monosaccharides undergo a condensation reaction which involves the elimination of a small molecule, such as water and from the functional groups only. The common examples of disaccharides are- sucrose, lactose, maltose, sophorose, turanose, rutinose etc.

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Both CH₃Cl and NH₃ have C₃v point group.

Monosubstituted benzene, when treated with an electrophile, undergoes electrophilic aromatic substitution reaction. Each reaction yields a disubstituted benzene as the product, which can be identified using the descriptors ortho, para and meta as products. Common ortho and para directing groups are:

• OH, - OCH₃, - NR₂, - CH₃, - NR₂ etc. Common meta directing groups are:
• NO, - SO₃H, - COCH₃, - CHO, - NO₂, - CN, - NR₃⁺ etc. Hence, only –OCH₃ group is ortho and para directing.

Phosphorus, present in an organic compound, is estimated by Carius method as magnesium pyrophosphate.

The molecules: CH₄, BCl₃, HCCH and (C₅H₅)₂Fe have point groups, Td, D₃h, D₂h and D₅h, respectively. Hence, the presentation of codes P - 3, Q - 1, R - 5, S - 4 is correct.

SO₂Cl₂ has C2v point group.

A monosubstituted benzene, when treated with an electrophile, undergoes electrophilic aromatic substitution reaction. Each reaction yields a disubstituted benzene as the organic product, which can be identified using the descriptors ortho, para and meta products. Common ortho and para directing groups are: -OH, -NR₂, -CH₃, -NR₂, etc. Common meta directing groups are: -NO, -SO₃H, -CHO, -NO₂, -CN, etc.

This is correct.

The regent/s for the name reactions; Perkin, Knoevenagel, Cannizzaro and Tischenko are Na/ CH₃COOH, Pyridine, Conc. NaOH and (C₂H₅)₃Al respectively. Hence, the codes P - 4, Q - 3, R - 1, S - 2 is the correct answer.

Since, equal weight of all electrolytes has been used. Higher the molecular weight, lower the number of moles and lower the magnitude of colligative properties like osmotic pressure. Molecular weight order is sucrose > glucose > urea. Hence, the order of osmotic pressures (p₁, p₂ and p₃) of the above solutions is urea (p₂) > glucose (p₁) > sucrose (p₃).

Cobalt gives blue colour of hot borax bead in borax bead test.