Is it permissible for a woman to wear underwear while performing Umrah?
Yes, it is permissible for a woman to wear underwear while performing Umrah. This is because she should keep her regular clothes that cover all her body while being in a state of Ihram (ritual consecration) for Hajj, or Umrah. However, she should uncover her face and hands, but it is permissible for her to let her head-covering garment drape from her head down over her face when non-Mahram (i.e., marriageable) men pass by her. And Allah Knows Best.
In life insurance with the Potash Company, enrollment is mandatory, and employees have the right to receive a cash amount from the insurance for surgeries and illnesses while employed by the company. Is the amount given by the insurance in this case permissible (Halal) or prohibited (Haram)?
Since the insurance is compulsory, then what the insurance company pays in return for medical treatment is similar to donation, and I pray to Allah The Almighty that this is lawful even if this service is deducted from your salary in return of it, so in this manner you take back some of the amount you paid in form of above treatment. And Allah Knows Best.
Is it permissible for a woman to shake hands with her brother-in-law?
It is forbidden for the woman to shake hands with her brother-in-law because he isn`t a Mahram (unmarriageable) of hers.
What is the semi-circular structure attached to the Holy Kabah?
The semi-circular structure attached to the Holy Kabah is Hijr Al-Kabah (is a low wall originally part of the Kabah) and passing behind it is an obligation while making Tawaf because it is a part of the Holy Kabah. And Allah Knows Best.