What is the coolest letter in the alphabet?

What does this Rebus Picture mean?

What is black when you buy it, red when you use it, and gray when you throw it away?

Find the next number in the series.
1 10 24 43 67 ?

You need to arrange three 7 and mathematical symbols to form number 1?

What has 13 hearts but no other organs?

What time is it when an elephant sits on a fence?

Two guards were on duty outside a barracks. One faced up the road to watch for anyone approaching from the North. The other looked down the road to see if anyone approached from the South. Suddenly one of them said to the other, "Why are you smiling?"

How did he know his companion was smiling?

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

It is a nine-letter word.
The exact opposite of the phrase "friendly and outgoing"
It contains the word "over".
It starts will a vowel.

What is it?