What does below chemistry rebus means?

Two girls were born to the same mother, on the same day, at the same time, in the same month and year and yet they're not twins. How can this be ?

Using the clues below, what four numbers am I thinking of?

The sum of all the numbers is 31.
One number is odd.
The highest number minus the lowest number is 7.
If you subtract the middle two numbers, it equals two.
There are no duplicate numbers.

John replied, when asked how old he was. In 2 years he will be twice as old as he was five years ago.' How old is he ?

It's a protector.
It sits on a bridge.
One individual can see directly through it, while others wonder what it hides.

What is it?

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?

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

What does this mathematical rebus means ?

An office is divided into 8 cubicles. How many of the cubicles are painted if only 1/8 of the cubicles are painted?

James bond was pushed out of an aeroplane without any parachute.
He survived, How come?