Write balanced equation for the redox reactions occurring between:
(a) An aldehyde (RCHO) and Tollen's reagent [Ag(NH3)2] + to form a carboxylic acid (RCO2H) and silver metal Ag'
(b) An aldehyde (RCHO) and chromic acid (H2CrO4) to form a carboxylic acid (RCO2H) and Cr 3+