Answer:
2. second-price, sealed-bid auction.
Step-by-step explanation:
In the given situation, it is mentioned that there is 25 risk -neutral bidders that contains the affiliated values and the same is to be allocated between $0 and $500 million
So, here the type of an action that could maximize the expected revenue is the second price i.e. sealed bid auction as in this the bidder provides the maximum price that received the good in the second maximum price
Therefore, the second option is correct