Why were most of the metals used in antiquity class (b) (soft, in HSAB terminology) metals?

 The most common source of mercury is cinnabar (HgS), whereas Zn and Cd in the same group occur as sulfide, carbonate, silicate, and oxide. Why?

 

Predict the reactions of the following hydrogen compounds with water, and explain your reasoning.

CaH2

HBr

H2S

CH4

 

Choose the stronger acid or base in the following pairs, and explain your choice.

CH3NH2 or NH3 in reaction with H+

Pyridine or 2-methylpyridine in reaction with trimethyl boron

Triphenylboron or trimethyl boron in reaction with ammonia