The textbook context directly poses this question and then discusses chlorophyll a in detail. It states that chlorophyll a is the 'chief pigment associated with photosynthesis' and is the 'major pigment responsible for trapping light.' The context also mentions that other pigments like chlorophyll b, xanthophylls, and carotenoids are called 'accessory pigments' that transfer energy to chlorophyll a, indicating chlorophyll a's primary and most abundant role.