Which process does not occur in $C_4$ plants?

Which one of the following is wrong in relation to photorespiration?

$C_2$ and $C_3$ cycles are predominantly found in:

Which of the following is the main product in the photorespiration of $C_3$ plants?

What effect would occur on photosynthesis if the amount of oxygen in the atmosphere decreases?

Assertion : Under conditions of high light intensity and limited $CO_2$ supply,photorespiration has a useful role in protecting the plants from photo-oxidative damage.
Reason : If enough $CO_2$ is not available to utilize light energy for carboxylation to proceed,the excess energy may not cause damage to plants.