The molecule that accepts electrons at the end of the light-dependent reactions is NADP+.
In the non-cyclic light reactions, electrons originate from water and move through Photosystem II, the cytochrome b6f complex, and Photosystem I. Light re-energizes the electrons at Photosystem I, after which ferredoxin and ferredoxin–NADP+ reductase transfer them to NADP+.
NADP+ accepts two electrons and a proton to form NADPH. This reduced electron carrier then supplies the reducing power needed by the Calvin cycle to convert carbon compounds into carbohydrates. ATP is produced alongside NADPH, but it stores and transfers energy rather than serving as the final electron acceptor.
Oxygen is also easy to confuse with the answer because it is released during the light reactions. However, oxygen comes from the splitting of water at Photosystem II and is a by-product, not the terminal electron acceptor in normal non-cyclic photosynthetic electron flow. In cyclic electron flow around Photosystem I, electrons return to the chain instead, so NADPH is not produced by that route.