Is it permissible to add the nutmeg to one`s food?

Using a little bit of the nutmeg for seasoning is permissible, but using a great deal of it is impermissible since it could lead to intoxication, and Islam has forbidden all intoxicants and stupefacients.

For passing time, my friends and I have called a famous diviner. She told me that somebody had cast a spill on me not to get married for the rest of my life. I didn`t believe her, but I can`t forget her words. How can I protect myself from such thing?

Praise be to Allah the Lord of the Worlds.

Dealing with diviners is forbidden and what you are suffering from is due to your having consulted that diviner. Have trust in Allah and ask Him for forgiveness, but rest assured that whatever Allah has decreed will take place. And Allah The Almighty Knows Best.

Am I permitted to perform more than one prayer within single ablution?

You are permitted to pray as many as you could within one ablution and to recite Quran so long as your ablution isn't nullified.

Is Iddah (waiting period) incumbent on an old lady whose husband had died?

Upon the death of the husband, Iddah is incumbent on the wife regardless of her age.