( ( ( ( ( Mercury ( ( ( has ( ( ( relatively weak ) bonds ) ( for ( a metal ) ) ) ) and ) ( melts ( at ( -39 ( degrees Celsius ) ) ) ) ) ) , ) so ) ( it ( is ( a ( ( liquid ( at room ) ) temperature ) ) ) ) ) . )
(ROOT (S (S (NP (NNP Mercury)) (VP (VP (VBZ has) (NP (NP (ADJP (RB relatively) (JJ weak)) (NNS bonds)) (PP (IN for) (NP (DT a) (NN metal))))) (CC and) (VP (VBZ melts) (PP (IN at) (NP (CD -39) (NNS degrees) (NNS Celsius)))))) (, ,) (IN so) (S (NP (PRP it)) (VP (VBZ is) (NP (DT a) (ADJP (JJ liquid) (PP (IN at) (NP (NN room)))) (NN temperature)))) (. .)))
Mercury has relatively weak bonds for a metal and melts at -39  degrees Celsius, so it is a liquid at room temperature.
(ROOT (S (NP (NNP Mercury)) (VP (VBZ is) (NP (NP (DT the) (CD one) (NN metal)) (SBAR (WHNP (WDT that)) (S (VP (VBZ melts) (PP (IN below) (NP (NN room) (NN temperature)))))))) (. .)))