What does below chemistry rebus means?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

Rebus Puzzle Definition: A rebus is an illusion device that uses pictures to represent words or parts of words.
What does This Rebus Puzzle Identify?

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

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

It is a nine-letter word.
The exact opposite of the phrase "friendly and outgoing"
It contains the word "over".
It starts will a vowel.

What is it?

Which country gets ill every time?

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