Is that an ongoing reaction in Red China? (5)
I believe the answer is:
chain
'reaction in red china?' is the definition.
'chain' can be an answer for 'reaction' (chain reaction is a kind of reaction). I'm not sure about the 'in red china?' bit.
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for chain that I've seen before include "Rope of metal links" , "a number of hotels" , "Shackle" , "Length of pitch" , "a sort of letter" .)