Does the clipping of nails nullify ablution?
No, it does not, and it is preferable to wash the hands afterwards.
Is it permissible for a woman to give the ransom (Fidyah) for breaking her fast to her granddaughter (her son`s daughter)?
Praise be to Allah, and peace and blessings be upon our Master, the Messenger of Allah.
It is permissible for a woman to give the ransom (Fidya) for breaking her fast in Ramadan to her granddaughter (her son’s daughter), provided that the girl is poor and her basic needs are not being met by the maintenance (Nafaqah) of those who are lislamically obligated to provide for her. And Allah the Exalted knows best.
Is Zakah (obligatory charity) due on land intended for selling?
Yes, lands intended for trade are valued, and Zakah is paid according to their estimated value after a lunar year had lapsed, but if the owner didn`t pay the due Zakah, then he should do so after selling them.
What is the ruling on istinja' after urination, and is it done with water and soap or with water only?
Istinja' from urine and stool is obligatory. It is permissible to perform istinja' with water alone, or with toilet paper alone. The best way is with toilet paper then water. If one wishes to suffice with one of them, then water is better. And Allah the Almighty knows best.