Which number should replace the question mark?

What does this rebus riddle mean?

What is always in front of you but can’t be seen?

Readers with high attention to detail can spot the cheater in the exam hall in 5 seconds. Are you one of them? Test your visual skills now!

Can you name an animal whose killing cannot be performed without spilling your own blood?

I am a mother. However, I never give birth.

I am a father. However, I never nurse my children.

Wandering is not possible for me, but standing still happens occurs rarely.

Who am I?

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?

Who are the happiest people in IPL match?

After teaching his class all about Roman numerals (X = 10, IX=9 and so on) the teacher asked his class to draw a single continuous line and turn IX into 6. The teacher's only stipulation was that the pen could not be lifted from the paper until the line was complete.

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?