Sugar produced in photosynthesis is converted into starch in

Which of the following pairs is incorrect?

Assertion: Photosynthetically,$C_4$ plants are less efficient than $C_3$ plants.
Reason: The operation of the $C_4$ pathway requires the involvement of only bundle-sheath cells.

Statement $P$: During the dark reaction of photosynthesis,ketotriose is synthesized.
Statement $Q$: The sugar present in the structure of $ATP$ is an example of a ketopentose sugar.

Under conditions of constant illumination,the compensation period for a whole aquarium would be of infinite length when:

$I.$ In $C_{3}$-plants,the Calvin pathway takes place in mesophyll cells.
$II.$ In $C_{4}$-plants,the Calvin pathway takes place in the mesophyll cells.
Which of the following statements is true?