Those things which render the Salaah invalid

Q: If your mucus/phlegm has become sweet because of something sweet you ate then will it be okay to pray in that condition? Like in Ramadan when everyone drinks milkshake and eats dates when they break their fast and then they just wash their mouth out with water and stand up for Maghrib Salah even though their mucus is still sweet and the back of their throat is still sweet. Sometimes your mucus remains pink even after you wash your mouth out. What happens if you swallow this pink mucus during salah? Is it sufficient to quickly rinse out your mouth with water before salah or should you wait until the sweet mucus goes away? Sometimes I only break fast with water then eat after I pray to avoid this problem. What is the best way to deal with this?

Q: In fajr farz on the last rakat I made a mistake and I believe I got kind of mad and smacked my lips in the salaah but then I fixed my mistake. Is this fine?

Q: If a person performed Salaah and a while after that realised that there was blood on his clothes and was not sure when it occurred or messed on the clothes, does Salaah have to be repeated? If yes, should wudhu also have to be repeated?

Q: My question is about part of the satr becoming exposed during salaah. If someone performs salaah in a t-shirt and his satr becomes exposed whilst going into ruku or sajda, does this have any effect on the salaah?

Q: Is it permissible to read nafl salaah whilst looking inside the Quran and reading?

Q: My father passed away 20 days ago. Alhamdollilah Allah Ta'ala gave me a lot of saber and I did not cry in front of anyone. But every time I pray namaz I just automatically cry. I don't know why this happens. I try so hard to control myself because I am scared that shaitan maybe making me cry. Is it ok to cry in namaaz?

Q: If a person applies Vaseline in his nose and thereafter begins his Salaah. During Salaah he sniffs and the Vaseline goes down his throat. What is the condition of his Salaah?

Q: Five minutes after salaah, when I go to the toilet, some times I observe that a drop of urine is evident on the tissue between the underwear. Now I want to ask that after all the precautions you mention, if I notice such a thing, would my namaaz be valid?

Q: If a person is holding a handkerchief in his hand and performing salaah due to his nose running, his postures in salaah will be slightly changed, e.g. in sajdah he will hold his hand sideways or upside down so the hanky doesn't touch the floor, and in qadah his hand will be slightly lifted off his thigh with the hanky in between. Is it permissible to do so? What other options are there?

Q: If a person is performing salaah and needs to check the time so as not to miss Takbir-e-oola.

1) Can he look at his wrist watch which may involve him having to move his kurtha and tilt his wrist in qiyaam?

2) If it is dark would it be permissible to press the light button with the other hand as well?