(1)- alpha particle , it's greater in mass
Atoms are made up of protons , electrons and neutrons ..,, Atoms of the same element with different number of neutrons are called isotopes. Saying that substance “contains only one type of atom “ really means that it contains only atoms that all have the same number of protons .
Oxygen is the only element in the list.
I believe your answer is C.
Hope this helps!