Doubts regarding urine drops

Q: Whilst I was urinating, I felt as though a drop may have touched my leg as I thought I felt it. The question I have is that I am unsure if there was urine on my trousers and I assumed they were clean and prayed my Salaah. Was my Salaah valid, and also, if a scenario like this occurred in future where I am unsure, should I assume that my clothes are clean or my clothes are dirty?

Pants below the ankles

Q:

1) If you pull up your pants to ensure that it remains above your ankles before going down for rukhu or sajda, does it break your salaat?

2) If your pants falls below your ankles while reading salaat, does it break your salaat?

3) If you perform salaat with your pants below the ankles, is your salaat valid?

4) what type of movements nullify salaat?

Singing "Tala Al Badru Alayna" at a soccer match

Q: At a soccer match on 20th February 2015 fans of a Saudi Arabian soccer team by the name of Ittihad FC 'sang' the nasheed "Tala Al Badru Alayna," and held up a scarf saying: "On Messenger of Allah my beloved." Muslims are getting excited by this, saying MashaAllah. Are these actions of the fans of the fans and the subsequent reaction of Muslims justified? If it is not, would you be kind enough to explain why?

Hadith question

Q: Is this hadith authentic? The Prophet (Sallallahu Alayhi Wasallam) said, 'Whoever recites 4 verses from the first part of Surah al Baqarah, the verse of the Throne, two verses after the verse of the Throne and three verses from the last part of Surah al Baqarah, Satan would never come near him or the members of his family on that day, and nothing he despises would come near him or the members of his family, and never are these verses recited over a madman without him regaining his consciousness' [Darimi 3249/A in the Book of Excellence of the Quran; an-Nasai in the Deeds during the Day and Night]; Ibn Hibban & Tabrani]

Hadith Question

Q: Is this Hadith authentic? "Whoever reads Surah Ikhlas 100,000 times would have bought himself from Allah, and a caller from Allah will announce in heaven and on earth: 'verily, so-and-so has been set free by Allah, so whoever owes him anything, let him claim it from Allah.'"