using four eights (8) and a one (1) and one mathematical symbol , create the number 100

Solve this riddle by finding the odd one out from the rest.

In a competitive exam, each correct answer could win you 10 points and each wrong answer could lose you 5 points. You sat in the exam and answered all the 20 questions, which were given in the exam.
When you checked the result, you scored 125 marks on the test.

Can you calculate how many answers given by you were wrong?

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

John’s parents have three sons: Snap, Crackle, and what’s the name of the third son?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

The following four words might seem abrupt to you. But you can make them meaningful by just adding vowels.
RDSH
GGPLNT
TMT
NN

Hint: All of them are vegetables.

What happened when the wheel was invented?

How many pluses should we put between the digits of 987654321 to get a total of 99, and where?

Can you identify if it's a murder or a suicide ?