Answer
(a) same
(b) option (II)
Work Step by Step
(a) We know that the weight of the block will be the same; it doesn't matter whether it is erect or inverted. Thus, the same mass will be supported by the water and as a result, the volume of water that should be displaced to float the block will be the same when it is inverted and the water level in the tank remains the same.
(b) We know that the best explanation is option (II) -- that is, the same mass is supported by the water in either case, and therefore the amount of displaced water is the same.
