Answer
a) $2Fe+6H_2O\rightarrow 2Fe(OH)_3+3H_2$
b) $Ca+2HCl\rightarrow CaCl_2+H_2$
c) $2H_2O\rightarrow 2H_2+O_2$
d) $CO+H_2O\rightarrow CO_2+H_2$
Work Step by Step
a) $2Fe+6H_2O\rightarrow 2Fe(OH)_3+3H_2$
b) $Ca+2HCl\rightarrow CaCl_2+H_2$
c) $2H_2O\rightarrow 2H_2+O_2$
d) $CO+H_2O\rightarrow CO_2+H_2$
All of the above reactions show different ways of how hydrogen can be obtained. Reaction c) represents the way hydrogen is obtained for industrial purposes, whereas reaction a) shows the way hydrogen is obtained for laboratory purposes. Being extremely exothermic, reaction b) is not usually used to obtain hydrogen.
