Rewrite the sentence "It's unsure if he will pass the exam" using "whether".

The most appropriate transformation of the original sentence "It's unsure if he will pass the exam" using "whether" is the first choice: "It is unsure whether he will pass the exam."

This option correctly maintains the original meaning while incorporating "whether," reflecting the uncertainty regarding his potential to pass the exam. The use of "whether" is particularly suitable here, as it is commonly used to indicate alternatives or choices, in this case, the possibility of passing the exam.

The other options alter the meaning or do not appropriately fit the structure needed. While some utilize "whether," they also include variations such as "may" or "if," which change the nuances of uncertainty in a way that is not present in the original sentence.