There are definite physical differences between an apple and any other type of fruit. The same is true for elements. There are physical and chemical differences between the different elements, so it is very easy to tell them apart. The differences among these varieties are more subtle. Slight changes in color, average size, sweetness, etc. are what separate the individual types, but they are still all apples.
Isotopes are the same as the different types of apples.
One point which must be kept in mind is that the word isotope does not imply radioactivity. There are isotopes which are radioactive and some which are not.