Question

Name the isotope used to treat
1) Cancer
2) Goiter

Answer 1

Isotope of cobalt is used to treat cancer.
Isotope of iodine is used to treat goitre.

Answer 2

Cobalt-60 isotope is used to treat cancer cells.

Iodine-131 isotope is used to treat the goiter diseases.

Explanation:

Isotopes are types of atoms which have "same atomic number" but different "number of neutrons". There is different atomic mass because different "number of neutrons" is present in the atom. Each isotope exhibits certain specific chemical and physical properties which are different from other isotope.  

Here, I-131 and Co-60 are radioactive isotope and can easily detect the movement in the body (tumor and thyroid gland) when it is introduced into the body.