thank you !
F.R.S cannot occur at benzene because it's electrons are
delocalised by resonance along the benzene ring and hence forming a
pi electron cloud, hence forming strong bonds between the C
atoms? can
help check proper phrasing, thanks !
heat(not only u.v.?) can also initiate the breaking of cl2 molecule
to form cl radicals?
First of all, don't use acronyms. Secondly, who told you this?
"F.R.S cannot occur at benzene because it's electrons are
delocalised by resonance along the benzene ring and hence forming a
pi electron cloud, hence forming strong bonds between the C
atoms."
That is not a correct explanation of why free radical
substitution occurs on the side-chain of benzene rather than along
the benzene ring itself. I don't want to spoil the fun for you
guys, go ask your school teacher or private tutor why, see if
he/she knows.
Yes, heating instead of UV light can also initial the presence
of free radicals. However, your syllabus wants to test you to see
if you know that UV light can accomplish this, and is more
appropriate under certain industrial conditions (ie. where for
various reasons you do not want high temperatures at this stage of
the reaction), so you must still write "UV light" for the
conditions in the A level exams, to generate free radicals.