Is it permissible for a wife to boycott (not to attend to his different needs) her husband?

It isn`t permissible for the woman to boycott her husband unless he is the reason behind that, and it is recommended that both spouses seek the advice of righteous people to make reconciliation.

What is the ruling on loudly sending prayers on the Prophet (PBUH ) after the call for prayer Athaan?

All perfect praise be to Allah, The Lord of The Worlds                                                                                                                                                            Sending prayers on the Prophet after Athaan is a Sunnah for the Mou`zen (caller for prayer ) and the hearer. However, there is no harm in doing it loudly after the end of Athaan, but sometimes, it shouldn`t so that people wouldn`t think that it is an integral part of the Athaan. And Allah Knows Best.

What is the Du`a (supplication) of Istikhara (guidance prayer)?

O Allah, I consult You as You are All-Knowing and I appeal to You to give me power as You are Omnipotent, I ask You for Your great favor, for You have power and I do not, and You know all of the hidden matters. O Allah! If you know that this matter (then he should mention it) is good for me in my religion, my livelihood, and for my life in the Hereafter, or he said: "for my present and future life" then make it (easy) for me. And if you know that this matter is not good for me in my religion, my livelihood and my life in the Hereafter, or he said: "for my present and future life" then keep it away from me and take me away from it and choose what is good for me wherever it is and please me with it."

What is the ruling on eating the food prepared by Christians friends knowing that their income comes from trading in alcoholic drinks?