Is a woman`s neck an Awrah (private part)?
All Perfect Praise is due to The Lord of The Worlds.
It is an Awrah, and it is forbidden for her to reveal it before non-Mahrams (Marriageable men). And Allah Knows Best.
Is prayer nullified by having thoughts while performing it?
Prayer isn`t nullified by having thoughts while performing it, provided that the praying person offers all of its pillars and meets all of its conditions. However, the reward decreases significantly in the absence of reverence since a praying person is rewarded according to the attentiveness of his/her heart during prayer.
My mother is 70 years old and wishes to perform Hajj and Umrah, as she has never done so before. However, she also takes care of my ill father and is afraid of falling ill herself. What should she do?
If this is the obligatory Hajj – meaning she has not previously performed Hajj or Umrah – then it is permissible for her to go even without her husband's approval. However, she must travel with a Mahram (a male guardian) or a trustworthy group of women, and she should leave someone to care for her husband and attend to his needs. And Allah Knows Best.
Is it permissible for a person who had vowed to give a certain amount of money to another, but didn`t find the latter to donate that money to the mosque?
In principle, the vowing person should abide by his vow as much as possible. Therefore, if he couldn`t find the person that he had made the vow for, then the vow itself is countless and nothing is due on its maker. However, if the latter happens to find the former later on then, he has to give him that money.