I have recently formatted my SD card as adoptable/internal storage in android nougat 7.0. There is a option of ejecting the card. My question is, if I eject the card, would I be able to use it by a card reader, or would the data be corrupted/deleted?
Your card cannot be read by a card reader, as it is encrypted , when you converted it to internal or adoptable-storage. This encryption covers your device (internal storage) and SD. You can read more about that in adoptable-storage wiki
If you eject the card, data is not corrupted on the card, but as Izzy pointed out, your device would be pretty much unusable, till you re- insert