Bromine, astatine, fluorine, iodine and chlorine: are they in order? (8)
I believe the answer is:
brothers
'fluorine iodine and chlorine are they in order?' is the definition.
The definition suggests an adverb but the answer is not.
'bromine astatine' is the wordplay.
'bromine' becomes 'Br' (Br is the chemical symbol for bromine).
'astatine' becomes 'others' (I am not sure about this - if you are sure you should believe this answer much more).
'br'+'others'='BROTHERS'
Can you help me to learn more?
(Other definitions for brothers that I've seen before include "See 8" , "Siblings (in arms or in law?)" , "(Roman Catholic) monks" , "Male relatives" , "Brethren" .)