$($i$)$ Using the diagram shown below:

$($a$)$ For the $Si{O}_2-A{l}_2{O}_3$ system, what is the maximum temperature that is

possible without the formation of a liquid phase?

$($b$)$ At what composition or over what range of compositions will this

maximum temperature be achieved?

Composition $($ mol$\%A{l}_2{O}_3)$