Which of the following is a compound? co2 ne o2 p4

Explanation:

Element is a pure substance which is composed of atoms of similar elements.It can not be decomposed into simpler constituents using chemical reactions.Example: neon , oxygen and phosphorous

Compound is a pure substance which is made from atoms of different elements combined together in a fixed ratio by mass.It can be decomposed into simpler constituents using chemical reactions. Example: water

d.) the average kinetic energy of the gas particles is greater in container b because its particles move faster.

i believe you are right for all except the 3rd ( look at sqdancefan his answer is much better)