Question

find the appositive. if it is nonrestrictive, set it off with commas. if it is restrictive, submit the text without making any changes.

every year, approximately thirty-five thousand people attempt to reach the summit of mount kilimanjaro the tallest free-standing mountain in the world.
fewer than half of these climbers actually succeed.

Explanation:

The phrase "the tallest free-standing mountain in the world" is a nonrestrictive appositive. It provides extra, non-essential information about Mount Kilimanjaro (we already know which mountain is being referred to, so this detail is supplementary), so it needs to be set off with commas.

Answer:

Every year, approximately thirty-five thousand people attempt to reach the summit of Mount Kilimanjaro, the tallest free-standing mountain in the world.
Fewer than half of these climbers actually succeed.