CBSE 12th Chemistry Question Paper 2023 (Set 2)

The alpha-helix is a common secondary structure of proteins, which are chains of amino acids linked by peptide bonds (polypeptides). Sucrose is a disaccharide, starch is a polysaccharide, and nucleotides form nucleic acids.

Amylose is a linear polymer of alpha-D-glucose units. These units are linked together by alpha-glycosidic linkages specifically between the C1 atom of one glucose molecule and the C4 atom of the next. Option A/B (C1-C6) refers to the linkages found in amylopectin at branching points.

The standard cell potential E°cell is calculated as E°cathode - E°anode. Here, the reduction of Ag+ occurs at the cathode (+0.80 V) and the oxidation of Fe occurs at the anode (-0.44 V). Thus, E°cell = 0.80 V - (-0.44 V) = 1.24 V.

For a first-order reaction, the rate constant k = 0.693 / t(1/2). Given t(1/2) = 30 minutes, k = 0.693 / 30 = 0.0231 / 10 = 0.0231 min^-1, which is 2.31 × 10^-2 min^-1. Note: calculation yields 0.0231, which corresponds to 2.31 × 10^-2. Checking the options provided, 2.31 × 10^-2 is the correct magnitude.

C6H5NH2 (Aniline) is the least basic because the lone pair on the nitrogen atom is delocalized into the benzene ring through resonance, making it less available for protonation compared to aliphatic amines or ammonia.