If Rajina's daughter is my daughter's mom, who am I to Rajina?

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

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

I am an eight letter word and I am a computer terminology.
The second, third and fourth letters make an animal.
The fourth, fifth, sixth, seventh and eighth letters make a weapon.
The first, second, third and fourth letters can be taken as an outcome of any exam.
The fifth, sixth, seventh and eighth letter combine to form a high end typing software.

Can you tell who am I ?

Here is what you have to do. You have to throw a ball as hard as you can but it must return back to you even if it does not bounce at anything. Also, you have nothing attached to the ball. There is no one on the other end to catch that ball and throw it back at you.

How will you do it?

Can you count the number of rectangles on a chessboard?

Optical Illusion: A cat is hiding in plain sight in the backyard. Only the most observant eyes can spot the cat in 7 seconds. Can you? Test your eye power now!

What is black when you buy it, red when you use it, and gray when you throw it away?

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

I am a type of room you cannot enter or leave. Raised from the ground below, I could be poisonous or a delicious treat. What am I?