Christina has four daughters, and each of her daughters has a brother. How many children does Christina have?

Can you count the number of lines in the below picture?

What animal walks on four legs in the morning, two legs during the day, and three legs in the evening?

Oedipus, the king of Thebes, figured out the answer to the riddle:

Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

I have an eye but still cannot see.

Who am I?

If you say my name, I will no longer exist. What am I?

Using eight eights and addition only, can you make 1000?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

Can you replace the question mark with the correct number?