How many mass extinctions have occurred since the origin of life on Earth?

According to $IUCN$,when a taxon is facing an extremely high risk of extinction in the immediate future,it is categorized as:

The current loss of biodiversity is considered to be the sixth extinction. How is this different from previous extinctions?

If the Bengal tiger becomes extinct,

Provide information on the history of species extinction and state its effects.

The impacts of loss of biodiversity may lead to:
$I$. Lowered resistance to environmental perturbation
$II$. Decrease in plant production
$III$. Increased variability in ecosystem processes like water use,pest/disease cycle,and plant productivity
$IV$. Increase in plant production
Choose the correct option.