Can any source of energy be pollution-free? Why or why not?
No, none of the sources of energy can be pollution free.
Exploiting any source of energy disturbs the environment in some way or the other.
A particular source of energy may cause less pollution than any other source of energy but it doesn’t mean that it is 100% pollution free.
For example, A device like solar cell maybe pollution free, but the assembly of the device would have caused some environmental damage.