Answer:
a. was assassinated in spite of freeing the serfs.
Explanation:
He freed serfs, and because of this he is counted as the most democratic Tsar. He was assassinated in march of 1881.
It cant be b because he was not a oppressive ruler.
It cant be c since his coronation was on 7 September 1856 the year the Crimean War ended.
And it could be d but a is more specific
Hope this helps :)