Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

Teacher ask the student

'Why are you standing on that chair in music class ?'.

what did student replied ?

In my garden, I have many trees but only one of them is the mango tree. In these mango trees, there are some mangoes(as expected).

But after a strong wind, there are neither mangoes on the tree nor on the ground. Explain?

I am a type of room you cannot enter or leave. Raised from the ground below, I could be poisonous or a delicious treat. What am I?

What number do you get when you multiply all of the numbers on a telephone's number pad?

A man is shown a portrait painting. He looks closely, then tells, “Brothers and sisters have I none, but that man’s father is my father’s son!” Who is the man in the portrait?

How is the moon similar to a dollar?

What can you hold in your right hand, but never in your left hand?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

It's a 7-letter word.
If we remove 1 letter from it, it remains the same.
If we remove 2 letters from it, it remains the same.
If we remove 3 letters from it, it remains the same.
If we remove all the letters from it, still it remains the same.
What is it?