If the transaction is confirmed in block 491405, then B.
If not yet confirmed on block 491405, then BTC gold will still get credited for address A right? Or will it be like floating bitcoin not belonging to any address?
The Bitcoin Gold snapshot includes all confirmed transactions as of height 491407. That means that if the transaction still hasn't been included in a block by that block height, the BTG will be credited to Address A.
Even though this airdrop seems like a scam to me (in the sense that the developers are just pre-mining money into their pockets), it could be worth something. So now that we're only 13 blocks away from the snapshot, I'm not moving any coins until it's done.
When you say confirmed transactions, does that mean 1 confirmation is enough?