Answer : 3. "3"
Explanation :

more will replace much because – more (Adv.) : in addition; to a greater extent (needs to be done/is desired) more → Comparative Degree much →Positive Degree most →Superlative Degree Look at the examples given below : People watch T.V. more than is needed. She needs to be given more time than is allotted. Hence, leaves more to be desired is the right usage.