Cat, one in a hundred, shows this kind of energy (6)
I believe the answer is:
atomic
'this kind of energy' is the definition.
'cat one in a hundred' is the wordplay.
'cat' becomes 'tom' (a tom is a male cat).
'one' becomes 'i' (Roman numeral).
'in' is an insertion indicator.
'hundred' becomes 'c' (Roman numeral).
'tom'+'i'='tomi'
'a'+'c'='ac'
'tomi' going into 'ac' is 'ATOMIC'.
'shows' is the link.
(Other definitions for atomic that I've seen before include "Relating to basic particles" , "Sort of energy or number" , "Basically simple" , "Relating to tiny particles" , "Sort of bomb, number, or power" .)