Which redox equation is correctly balanced? (1) cr3+ + mg -> cr + mg2+ (2) al3+ + k -> al + k+ (3) sn4+ + h2 -> sn + 2h+ (4) br2 + hg -> hg2+ + 2br

Given the following at 25c calculate delta hf for hcn (g) at 25c. 2nh3 (g) +3o2 (g) + 2ch4 (g) > 2hcn (g) + 6h2o (g) delta h rxn= -870.8 kj. delta hf=-80.3 kj/mol for nh3 (g), -74.6 kj/mol for ch4, and -241.8 kj/mol for h2o (g)