Chemistry

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(b, d) Receptor proteins are embedded in the cell membrane and their active sites project outside region of the cell membrane. Shape of the receptor changes during the attachment of messenger.

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(b) Artificial sweeteners are non-caloric substitutes for sugar. They are often intensely more sweet than sugar but do not enhance nutritional value of food. Vitamins and minerals are essential nutrients because they perform hundreds of roles in the body.

Amino acids will also enhance the nutritional value of food.

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Ans: (C)

In the process of nitration of benzene, firstly H₂SO₄ dissociates into H⁺ and HSO₄−. The proton produced further reacts with HNO₃ to give a positively charged complex that is unstable and dissociates into nitronium ions and water as products. The nitronium ion is an electron-deficient species i.e. electrophile that attacks the electron cloud of the benzene ring.

H₂SO₄  (conc.) ? H⁺+HSO₄⁻

H⁺+HNO₃? H₂NO₃⁺

H₂NO₃⁺? NO₂⁺ + H2O

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Ans: (B) 

Primary aliphatic amines react with nitrous acid to form aliphatic diazonium salts, which are unstable and release nitrogen gas and alcohol quantitatively.

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(d) Sucralose is an artificial sweetening agent which is 600 times sweeter than sucrose and does not provide calories.

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(c) Inhibitors are chemical substances which tend to reduce the activity of a particular enzyme. Generally, a weak bond such as H-bonding, van there Waals interaction, etc. is formed between the enzyme and the inhibitor.

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Ans: (C)

Methyl amine reacts with HNO₃ form methanol with release of nitrogen gas and water as side products.

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(c) Drugs usually interact with biomolecules such as carbohydrates, lipids, proteins and nucleic acids. These are called drug targets. Vitamins are not a target molecule for drug function in body.

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Ans: (D) 

The greater the electron density towards the ring, the greater its basic strength.

The electron withdrawing group reduces basic strength, whereas the electron donating group increases basic strength.

This is a multiple choice answer as classified in NCERT Exemplar

(c) Polyethyleneglycols are used in the preparation of non-ionic detergents.