If 100 atoms of element Y contain 60 atoms of 9Y and 40 atoms of 11Y, calculate the relative atomic mass (one decimal place) of Y​

Which element below could be and isotope of this atom

The image below shows a weather service map.. i’m not sure if is correct

An isotope undergoes radioactive decay. the new isotope that forms has an atomic number fhat is 2 less than the original isotopes. which kind of decay has occured and how do you know