Chemistry MCQs for NEET — Practice Questions with Answers

The context mentions that 'It has been observed that half filled and fully filled degenerate set of orbitals acquire extra stability due to their symmetry'. (Reference: 'It has been observed that half filled and fully filled degenerate set of orbitals acquire extra stability due to their symmetry (see Section, 2.6.7).')

For 4s: n=4, l=0, so (n+l) = 4+0 = 4. For 3d: n=3, l=2, so (n+l) = 3+2 = 5. According to the (n+l) rule, the lower the (n+l) value, the lower the energy. Therefore, 4s (n+l=4) has lower energy than 3d (n+l=5). (Reference: 'the lower the value of (n + l) for an orbital, the lower is its energy.')

The context states: 'The secondary structure of protein refers to the shape in which a long polypeptide chain can exist. These structures arise due to the regular folding of the backbone of the polypeptide chain due to hydrogen bonding between $C=O$ and $-NH-$ groups of the peptide bond.'

The context mentions: '$\alpha$-Helix is one of the most common ways in which a polypeptide chain forms all possible hydrogen bonds by twisting into a right handed screw (helix) with the –NH group of each amino acid residue hydrogen bonded to the C=O of an adjacent turn of the helix.'

The context states: 'In $\beta$-pleated sheet structure all peptide chains are stretched out to nearly maximum extension and then laid side by side which are held together by intermolecular hydrogen bonds. The structure resembles the pleated folds of drapery and therefore is known as $\beta$-pleated sheet.'

The context explains: 'The tertiary structure of proteins represents overall folding of the polypeptide chains i.e., further folding of the secondary structure. It gives rise to two major molecular shapes viz. fibrous and globular.' and 'Tertiary structure is absolutely necessary for the many biological activities of proteins.'

The context details: 'The main forces which stabilize the 2° and 3° structures of proteins are hydrogen bonds, disulphide linkages, van der Waals and electrostatic forces of attraction.'

The context provides: 'Globular proteins... Insulin and albumins are the common examples of globular proteins.'

The context states: 'Some proteins are an assembly of more than one polypeptide or subunits. The manner in which these individual folded polypeptides or subunits are arranged with respect to each other... is the architecture of a protein otherwise called the quaternary structure of a protein. Adult human haemoglobin consists of 4 subunits.'

The context explains: 'When a protein in its native form, is subjected to physical change like change in temperature or chemical change like change in pH, the hydrogen bonds are disturbed. Due to this, globules unfold and helix get uncoiled and protein loses its biological activity. This is called denaturation of Proteins.'