Which enzyme joins Okazaki fragments? A. Helicase B. Primase C. DNA ligase D. Topoisomerase Explanation: DNA ligase seals nicks in the sugar-phosphate backbone.
During DNA replication, the leading strand is synthesized: A. Continuously in the 5' to 3' direction B. Continuously in the 3' to 5' direction C. Discontinuously away from the fork D. Only after lagging strand is completed Explanation: DNA polymerases extend only 5' to 3', allowing continuous synthesis toward the fork on one template.
Which biomolecule directly stores hereditary information in most organisms? A. Protein B. DNA C. Lipid D. Polysaccharide Explanation: DNA encodes genetic information in nucleotide sequence.
Which gas deviates most from ideal behavior at high pressure and low temperature? A. One with negligible intermolecular attraction and molecular volume B. One with significant intermolecular attractions and finite molecular volume C. A hypothetical point-particle gas D. Any gas behaves ideally under all conditions Explanation: Real-gas deviations become strong when attractions and excluded volume matter.
Which crystal defect preserves stoichiometry in ionic solids? A. Frenkel defect B. Metal excess defect only C. Metal deficiency defect only D. Substitutional alloying Explanation: In a Frenkel defect an ion shifts position without changing overall composition.
Which statement is correct for a buffer solution? A. It resists all pH changes regardless of added amount B. It contains a strong acid and strong base in equal amounts C. It resists pH change upon small addition of acid or base D. Its pH is always 7 Explanation: Buffers work through conjugate acid-base pairs that neutralize small perturbations.
The pH of a neutral aqueous solution at 25°C is: A. 0 B. 7 C. 10 D. Depends only on solute mass Explanation: At 25°C neutral water has ([H^+] = [OH^-] = 10^{-7},\text{M}).
Which statement about hydrogen bonding is correct? A. It occurs only in hydrocarbons B. It requires hydrogen bonded to highly electronegative atoms such as N, O, or F C. It is weaker than all London forces D. It is a covalent bond between two molecules Explanation: Strong intermolecular hydrogen bonding needs a polarized H attached to N, O, or F.
Which functional group is present in an ester? A. (-COOH) B. (-COOR) C. (-CHO) D. (-CONH_2) Explanation: Esters contain an acyl group bonded to an alkoxy oxygen.
Aromaticity requires a cyclic, planar, conjugated system containing: A. (4n) (\pi) electrons B. (2n) (\sigma) electrons C. (4n+2) (\pi) electrons D. Any even number of (\pi) electrons Explanation: Hückel’s rule specifies (4n+2) delocalized (\pi) electrons for aromatic stabilization.