Give the name of a metal which reacts with hot water

Explain the following: 

Gold and silver are mixed to make ornaments. 

Explain the following: 

Sodium is preserved in kerosene. 

The elements $\mathrm{X}, \mathrm{Y} \& \mathrm{Z}$ react as follows. 

${\mathrm{X}}_2{\mathrm{O}}_3+2\mathrm{Y}\to {\mathrm{Y}}_2{\mathrm{O}}_3+2\mathrm{X}$

${\mathrm{Y}}_2{\mathrm{O}}_3+3\mathrm{C}\to 3\mathrm{CO}+2\mathrm{Y}$

Arrange the elements $\mathrm{X}, \mathrm{Y} \& \mathrm{Z}$ in the order of their decreasing reactivity.

Note:'This question given in the book seems to have error and the modified question should be as given below'

The elements $\mathrm{X}, \mathrm{Y} \& \mathrm{Z}$ react as follows. 

${\mathrm{X}}_2{\mathrm{O}}_3+2\mathrm{Y}\to {\mathrm{Y}}_2{\mathrm{O}}_3+2\mathrm{X}$

${\mathrm{Y}}_2{\mathrm{O}}_3+3\mathrm{Z}\to 3\mathrm{ZO}+2\mathrm{Y}$

Arrange the elements $\mathrm{X}, \mathrm{Y} \& \mathrm{Z}$ in the order of their decreasing reactivity.