Compare numbers in two columns in Excel

I appreciate any response to help me with this.

I have two columns of numbers
A B
B.121 S.222
S.154 B.121
B.164 S.154
B.187 B.154

I have about 100 lines of this data on multiple tabs (roughly 1000 or so in total)
Both columns have essentially the same numbers but column B has multiple instances of the same number. Column A is unique

I need to ascertain if every number in Column A is present in Column B at least once
and i need to know the number that's missing from column B.

Thanks a lot.