$8.$ Which cell type is used in the electrolysis of brine to produce caustic soda?

$-$ a$)$ Mercury cell

$-$ b$)$ Diaphragm cell

$-$ c$)$ Membrane cell

$-$ d$)$ All of the above

$9.$ What is the primary disadvantage of using mercury cells in brine electrolysis?

$-$ a$)$ High energy consumption

$-$ b$)$ Mercury pollution

$-$ c$)$ Low efficiency

$-$ d$)$ Complex operation