Why Aeroplane windows are round?

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

What am I?

If it took eight men ten hours to build a wall, how long would it take four men to build it?

What is full of holes but still holds water?

I never was there, I am always to be.
You have never ever seen me, not ever you will.
Yet I am the confidence of everyone.

Who Am I?

An inspection by the superintendent of St. Joseph School was scheduled on the next day. The class teacher Jenifer knew that he would be asking questions from her class and she would have to choose a pupil to answer. To offer a perfect impression over him, the teacher explained certain instructions to the students to maximise the chances of getting correct answer every time.

What did she say to the students?

Count the squares in the matchstick puzzle below?

The answer I give is yes, but what I mean is no. What was the question?

Rearrange the letters in "new door" to make one word.