Solution:

I'm a jigsaw puzzle piece.

Solution:

45

1/5 of 45 = 9
9 + 45 = 54

Solution:

11

Solution:

Over My Dead Body

Solution:

35

Explanation
4 : 1/2 X 1/2 matchsticks squares
17: 1X1 matchsticks squares
9 : 2X2 matchsticks squares
4 : 3X3 matchsticks squares
1 : 4X4 matchsticks squares
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35

Solution:

They are sunglasses (sit on the bridge of your nose)

Solution:

Simple, the slow ones are in prison :-)

Solution:

I am spoons/plate (more answer possible)

Solution:

she cant find 11 on phone.

Solution:

5 questions

Explanation:
This question can be solved using a simple trick. If all the questions were answered correctly, the student would have 200 chocolates.
For every wrong answer, he will lose 5 chocolates and he will also lose 10 chocolates that he would have gained if he would have answered correctly. Thus, for every wrong answer, you have to deduct 15 chocolates from 200.
200 - 125 = 75
15 * 5 = 75
Hence, he gave wrong answer for 5 questions.