Transition state structure of the substrate formed during an enzymatic reaction is 
(a) Transient but stable
(b) Permanent but unstable
(c) Transient but unstable
(d) Permanent and stable
(c) The substrate binds to the enzyme at its active site forming an enzyme substrate complex. This complex formation is a transient and unstable phenomenon. Very soon, the product is released from the active site. It is the fact that all other intermediate structural states are unstable. Stability is related to energy status of the molecule or the structure.