7Li.
It is one of the Primordial_elementsor, more properly, primordial isotopes, produced in Big Bang nucleosynthesis. Thus it is more abundant.
The most common isotope of lithium is lithium-7. It makes up about 92.5% of naturally occurring lithium.
The most abundant isotope of arsenic is arsenic-75.
Bolivia and Chile
There is only one abundant isotope of fluorine and that is 19FFluorine-19 is the most common isotope, its abundance is classed as 100% because no other Fluorine isotopes exist in significant quantities. It is also the only stable Fluorine isotope.
Potassium I reckon
The most common isotope of lithium is lithium-7. It makes up about 92.5% of naturally occurring lithium.
The most abundant isotope of arsenic is arsenic-75.
The most abundant isotope of hydrogen is protium, which has a single proton and no neutrons in its nucleus. It accounts for about 99.98% of all naturally occurring hydrogen.
Bolivia and Chile
Lithium!
There is only one abundant isotope of fluorine and that is 19FFluorine-19 is the most common isotope, its abundance is classed as 100% because no other Fluorine isotopes exist in significant quantities. It is also the only stable Fluorine isotope.
Lithium-isotope 6 has 3 neutrons. Lithium-isotope 7 has 4.
Potassium I reckon
An isotope of cobalt is used to to kill cancer cells. The isotope americium-241 is used in smoke detectors.
The most frequent isotope of lithium has 4 neutrons.
Carbon-12 is the most abundant isotope of carbon, making up about 98.9% of carbon found in nature. Carbon-13 is the second most abundant isotope, making up about 1.1% of natural carbon.
Lithium has two stable isotopes, lithium-6 and lithium-7. There are also several radioactive isotopes of lithium, with lithium-8 being the most common radioactive isotope.