What does below chemistry rebus means?

Two prisoners Jack and Jill are locked in a cell.
There is open window approx 40 feet above the ground of the cell.
They are never able to reach there.

Then they plan to escape by a tunnel and they start digging out.
After digging for more than 20 days, Jill comes with the different plan and they escaped.

what was the plan ?

We are a group of eight brothers. We consider the weak, yet we protect the king in every battle. If we move ahead, we never turn back. Who are we?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

What question can you never answer yes to?

Why do we preferably have round manhole covers and not square ones?

What happened when the wheel was invented?

O_er_t_o_

Complete the missing letters of the given word.

Find the next number in the series?
2, 12, 36, 80, 150, 252, 392, _ ?

Look at the below sequence of letters and tell us what the next letter should be:

O T T F F S S ?