It's called a compound because different elements are held together by a chemical bond.
Very small pka. can also be - pka.
I am pretty sure it is Vitamin A... but I could be wrong. Sorry if it is wrong.
Explanation:
Group 16 elements are oxygen family elements also called as chalcogens.This name is given for the their ore forming abilities. It consists of the elements oxygen, sulfur, selenium, tellurium and polonium.
Group 16 have six electron in the outermost principal energy level or the valence shell and their general electronic configuration is ns2 and np4.
