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

I’m tall when I’m young, and I’m short when I’m old. What am I?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

He does not have any heart but still, He manages to live.
If you kill him, you will eventually die but yet you kill him.
He cannot run, who is He?

Known by all without exception, Forever here, for your protection, Sometimes strong, sometimes weak, Right after the night I come - hot and chic. And while millions of miles away, I always get to you, I find my way. No life around could do without me, Can you guess what I might be?

Give it food and it will live; give it water and it will die.

Always in you, Sometimes on you;

If I surround you, I can kill you.

What am I?

A man calls his dog from the opposite side of a river. The dog crosses the river without a bridge or a boat and manages to not get wet. How is this possible?

I have an eye but still cannot see.

Who am I?

How many letters are in the alphabet?