Which statement describes a physical change?
a.
sodium metal reacts explosively with oxygen.
b.
lead is heated and becomes more viscous.
c.
calcium is added to acid and hydrogen gas is produced.
d.
iron combines with oxygen to form rust.

An engineer decides to use a slightly weaker material rather than a stronger material, since she knows that the stronger material can break suddenly. this is an example of what? a choosing a material that will show warning before it fails b using composite materials that combine strength c using a material for multiple applications d using design techniques that increase efficiency and reduce cost