When I get multiplied by any number, the sum of the figures in the product is always me. What am I?

The dirtier I get, the whiter I look. Who am I?

How many sides does a circle have?

If an electric train is travelling south, then which way is the smoke going?

What you cannot hold but it is yours?

How many letters are in the alphabet?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

What breaks yet never falls, and what falls yet never breaks?

They do not possess flesh or feathers or scales or bone
But still, they are blessed with fingers and thumbs of their own.

In an interview, a boy was asked an unusual question 'How two persons sitting with a table in between them can't see each other?' He was unable to reply. Can you?