What is common among 11, 69, and 88?

Imagine you are in a room with no windows or doors. How will you get out?

Its something that each of us devours,
Not just us but birds, beats, trees, and flowers,
Frets iron and nibbles steel,
Toil hard stones to meal,
Exterminates king, collapse town,
And blows the mountains down.

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

In a mathematical quiz, you are asked the following question:

Use three 9s in a mathematical expression without dividing or multiplying to form the number one.

Can you answer the question?

I have Rs.50 and I spend it in the way as below.

You need to arrange three 7 and mathematical symbols to form number 1?

You are provided with a grid (as shown in the picture). Can you fill the squares with numbers 1-8 in a manner that none of the two consecutive numbers are placed next to each other in any direction (vertically, horizontally or diagonally?)

A word I know has six letters it contains, remove one letter and 12 remain. What is it?

If in a car race, the man who came two places in front of the last man finished one ahead of the man who came fifth, how many contestants were there?