Here is a link to a website that explains these observed trends.
https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Book%3A_Introductory_Chemistry_(CK-12)/06%3A_The_Periodic_Table/6.15%3A_Periodic_Trends%3A_Atomic_Radius
There is Kinetic energy involved in the state something is in. The molecules in a liquid are moving around quicker than those in a solid.
That's one reason.
The ice requires energy to melt. Bonds must be broken to get from a solid to a liquid.
Your answer is C hope that helped
This is the answer (C): Co2