Question

At the beginning of an experiment a scientist proposes an educated guess about will happen. What is this guess called?

Answer 1

`"An hypothesis..."`

Explanation:

To quote a dictionary of philosophy...

…`" an hypothesis is a proposition made as a basis"` `"for reasoning, without any assumption of its truth..."`

The hypothesis is then tested in an experiment..to determine its validity and scope. A scientific hypothesis is `"falsifiable"`...See here and here.