<span>Phase, color, and ductility are all examples of physical external properties</span>
This is weird.
All three 'choices' are true.
Line um up. (a) shows how to solve the problem. (b) does it. and (c) is the answer.
The formula for the mass that remains:

m₀ - the initial mass, t - time, T - the half-life

The answer is c. 1.25 g.
All objects in orbit must follow the path of an ellipse (one of Keplers laws)