The correct choice is C .
Technically, choice-A is the process involved. But it's already been done,
and widely published, and the spectrum of every element is easily available.
For you to take the time and go to the trouble of constructing the spectra
would be like inventing wheels if you want to ride a bicycle.
Physical change is changing physically it eg appearance while chemical change is the molecular bonds water is always defined as H2O and not change chemically. Hope this answers your question.
C it reduces the amount of useful work done on objects move it up the ramp
