What is common among 11, 69, and 88?

What does below chemistry rebus means?

The ages of a father and son add up to 66.
The father's age is the son's age reversed.
How old could they be?
(3 possible solutions).

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

What has a ring but no finger?

I can write cow in 13 letters.

Can You?

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

Find out the missing number in the picture attached:

Can you make four (4) nines (9) equal 100?

A woman is sitting in her hotel room and hears a knock at the door. She opens the door to see a man whom she’s never met before. He says, “I’m sorry, I have made a mistake, I thought this was my room.” He then goes down the corridor and into the elevator. The woman goes back into her room and calls security. What made the woman so suspicious of the man?