Mystery of hydrogen bond regularly seen in white element (8)
I believe the answer is:
whodunit
'mystery' is the definition.
('whodunit' can be a synonym of 'mystery')
'hydrogen bond regularly seen in white element' is the wordplay.
'hydrogen' becomes 'h' (H is the chemical symbol for hydrogen).
'regularly' indicates alternate letters (regularly take one letter, leave next etc.).
'seen in' means one lot of letters goes inside another.
'white' becomes 'w'.
'element' becomes 'unit' (I've seen this before**).
The alternating letters of 'bond' are 'od'.
'h'+'od'='hod'
'w'+'unit'='wunit'
'hod' put into 'wunit' is 'WHODUNIT'.
'of' is the link.
(Other definitions for whodunit that I've seen before include "'A crime novel, colloquially (8)'" , "American-style murder story" , "Informally, a detective story or play" , "Murderer revealed at the end, US style" , "thriller" .)