-they are inside the nucleus of an atom
- they have a relative charge of +1
- they have a relative mass of 1

If the half-life of a sample of a radioactive substance is 30 seconds, how much would be left after 60 seconds? <span>
A. one-fourth</span>
Cobalt sulphate is the usual source of water-soluble cobalt since it is the most economical salt and shows less tendency to deliquesce or dehydrate