Railroad Crossing, look out for the cars. Can you spell that, without any R's ?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

Three fair coins are tossed in the air and they land with heads up. Can you calculate the chances that when they are tossed again, two coins will again land with heads up?

With pointed fangs I sit and wait; with piercing force I crunch out fate; grabbing victims, proclaiming might; physically joining with a single bite. What am I?

When it's bad luck to meet a black cat?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

"That Restaurant always remains crowded. This is the reason why nobody goes there".

Can you find a flaw in this statement?

I look at you, you look at me, I raise my right, you raise your left. What am I?

You are mixing a mixture of cement and Sand with five gallons of water. You have a garden hose giving you all the water you need. The problem is that you only have a four-gallon bucket and a seven-gallon bucket and neither has graduation marks. Find a method to measure five gallons.

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?