Solve the following series:
AZ, GT, MN, __, YB

You are trapped in a room with two doors. One leads to certain death and the other leads to freedom. You don't know which is which.
There are two robots guarding the doors. They will let you choose one door but upon doing so you must go through it.
You can, however, ask one robot one question. The problem is one robot always tells the truth, the other always lies and you don't know which is which.
What is the question you ask?

In the given figure, you can see that four match sticks are used to form a square. Can you form five squares by using six matches?

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

A man who was outside in the rain without an umbrella or hat didn’t get a single hair on his head wet. Why?

The more you take me, the more you leave me behind.
Who Am I?

Why is a river so rich ?

If you say my name, I will no longer exist. What am I?

When it is alive we sing, when it is dead we clap our hands. What is it?

If you read clockwise, you can form a word by inserting three missing letters in the picture given below. Can you do it?