Suggest reasonable explanations for each of the following observations. (a) Both hydrogens are anti to each other

Question:

Suggest reasonable explanations for each of the following observations.
(a) Both hydrogens are anti to each other in the most stable conformation of formic acid.
(b) Oxalic acid has a dipole moment of zero in the gas phase.
(c) The dissociation constant of o-hydroxybenzoic acid is greater (by a factor of 12) than that of o-methoxybenzoic acid.
(d) Ascorbic acid (vitamin C), although not a carboxylic acid, is sufficiently acidic to cause carbon dioxide liberation on being dissolved in aqueous sodium bicarbonate.