There is a shortcut to this Chem question. simply look at this problem as if it were a cooking recipe. you have 7 parts Carbon and 18 Parts Hydrogen for a total of 25 parts. Simply divide 5.2 by 25 then multiply by 7 to get your answer.
(5.2/ 25) 7 = 1.456 moles
An isotope is when there is same amount of atomic number but different mass number. It also mean that only the number of neutrons changes if there is an isotope present.
Trisulfer-dodecacarbonide
(maybe)
It is an approximation of its mass number. Each isotope of an element has a different mass number.
