Question

Why do transition metals often have more than one possible ion, and why we distinguish these ions in the form of roman numerals in brackets?

Answer 1

Answer: The number in brackets indicates how many electrons have been lost.

Step-by-step explanation:

Answer 2

They have variable Oxidation States, meaning they can undergo reduction to oxidise some other species or they can undergo oxidation to reduce some other species.
To my understanding, for A-levels, they can change oxidation states as they lose the s-orbital electrons before losing d-orbital electrons and the 5 d-orbitals are not all at the same energy.
With regards to using roman numerals, I believe it's just traditional convention.