Is it permissible for a young lady to wear a short skirt, which is above her knee, over pants?
                                All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is His slave and Messenger.
In Islam, it isn`t permissible for a woman to wear garment revealing her beautiful shape and arousing men`s sexual desire. This is whether the garment is transparent or skin-tight showing the size of her private parts. A Muslim woman`s garment must be loose and not revealing since she will be accountable for this before Allah The Almighty on the Day of Judgement. And Allah The Almighty Knows Best. 
                             
                        
                            
                                
                                Is it permissible to make ablution without answering the call of nature after waking up?
                                Washing front and back openings (Istinjaa`) is not a condition for the validity of ablution because it is done to remove Najaasah (impurity), thus if there is no Najaasah, there is no need for that, and then it is permissible to make ablution without answering the call of nature. However, prayer is invalidated if there is Najaasah on the anus ,or the front opening, so it (Najaasah) must be removed for the prayer to become valid, and not the ablution.
                             
                        
                            
                                
                                Is Iddah (waiting period) incumbent on an old woman whose husband had died?
                                Upon the death of the husband, Iddah is incumbent on the wife regardless of their age. And Allah Knows Best.
                             
                        
                            
                                
                                I made a vow "If the Israeli troops retreated out of Gaza strip I will buy a cake from a certain bakery" and it happened. Am I obliged to buy from the same bakery?
                                You are obliged to buy from the same bakery. And Allah Knows Best.