I suffer from absentmindedness and constant worries during prayer, what should I do?
You should take refuge in Allah from the whispers of the devil and life worries. You should also seek Allah`s help and offer a lot of Istigfar (seeking the forgiveness of Allah). And Allah Knows Best.
Should nail polish be removed before making ablution?
Yes, it should be removed because it prevents water from reaching the nails.
Does passing wind, from the anus without a smell, invalidate prayer?
If a person is certain of having passed wind even if it was with no smell, then both his/her ablution and prayer are invalidated, thus he/she should remake ablution and re-perform prayer.
Is buying and storing gold bars for profit permissible or prohibited?
Buying and storing gold bars for profit is permissible, and there is no harm in it. And Allah The Almighty Knows Best.