Unmarried woman taking an oath that if she does something then her nikaah will break

Q:

1. If before giving the marriage consent in front of witnesses a girl takes an oath that if she does a certain thing her nikaah is invalid but she breaks the above oath when she is married ...is her nikaah valid?

2. If after giving the marriage consent in front of witnesses a girl takes an oath that if she does a certain thing her nikaah is invalid but she breaks the above oath when she is married ...is her nikaah valid?

Seeing a white spot on one's underwear

Q: Sometimes when I go to the bathroom I see a white spot/stain. The thing is that the stain is there when I am awake. I mean that if I don't sleep for a whole day and then see it is there. Even If I don't get aroused there is a spot. It doesn't feel wet and neither does my private part fell sticky or slimy like its covered nether does my skin. This case is when I haven't slept for whole day after changing underwear in morning. I don't even feel anything if it there or while coming out if something does come out

1. Am I impure?

2. Do I have to change my underwear and do I have to do ghusul?