Very precise about hydrogen for specialists (5)
I believe the answer is:
niche
'very precise about hydrogen for specialists' is the definition.
I can't judge whether this definition defines the answer.
'very precise about hydrogen' is the wordplay.
'very precise' becomes 'nice' (similar in meaning. I am not sure about the 'very' bit.).
'about' is an insertion indicator.
'hydrogen' becomes 'H' (H is the chemical symbol for hydrogen).
'nice' going around 'h' is 'NICHE'.
Can you help me to learn more?
(Other definitions for niche that I've seen before include "Position well suited to the occupier" , "Chine (anag) - suitable place in life" , "Recess; place in life" , "Specialized market" , "Shallow recess in a wall" .)