Which number should replace the question mark?

Give it food and it will live; give it water and it will die.

Once while in his court, King Akbar asked Birbal to write something on a wall that makes one sad when read in good times and makes one happy when read in sad times.

He took only a few moment and wrote something that fit the requirements. What did he write?

By adding four matchsticks, can you divide the square shown in the picture into two equal parts?

Can you move from MANILA to UGANDA in the shortest time? You need to follow the below rules:
Rule 1: You can change up to 3 alphabets at a time.
Rule 2: New words must be of 6 alphabets.
Rule 3: The new word formed must be a country or capital.

You balance a broom horizontally on your finger such that your finger is present at the centre of the gravity of the broom (precisely). You mark the spot and cut the broom into two halves. You are left with two pieces - one long piece with the handle and one short piece with bristles and a portion of the handle.

If you weigh both the pieces now, what will happen?
a) The longer piece weighs more.
b) The shorter piece weighs more.
c) Both pieces weigh equally.

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?)

What is the probability of getting five Mondays in a 31-day month?

There are two arch enemies Messi and Ronaldo who hate each other to an extreme. One day both were going together and a Jeanie appeared in front of them. Jeanie grants 3 wishes to Ronaldo and one to Messi.

Messi replied smartly 'Give me twice whatever Ronaldo demands'.

Ronaldo asked his 1st wish 'Give me 10000 billion dollars. Soon Messi gets 2000 billion dollars.
Ronaldo asked for his 2nd wish 'Give me one mansion in every country in the world. Soon Messi gets two mansions in every country of the world?

What should be Ronaldo's third wish?

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.