AP BIOLOGY

Detailed explanation-1: -hydrogen. Covalent bonds occur within each linear strand and strongly bond the bases, sugars, and phosphate groups (both within each component and between components). Hydrogen bonds occur between the two strands and involve a base from one strand with a base from the second in complementary pairing.

Detailed explanation-2: -The hydrogen molecule is the simplest substance having a covalent bond. It forms from two hydrogen atoms, each with one electron in a 1s orbital. Both hydrogen atoms share the two electrons in the covalent bond, and each acquires a helium-like electron configuration.

Detailed explanation-3: -Usually three classes are distinguished: weak, moderate, and strong bonds, with energetic boundaries at about 2 and 15 kcal/mol. The weak hydrogen bonds involve less polar X-H groups in proton donors, like C-H or P-H groups, or less polar acceptors, like the N2 molecule in the N2⋯HF complex discussed above.