Compare data on 2 separate worksheets and pull a reference cell

I have on inventory sheet that has all the data in each cell 2612 to be exact! That changes month to month with deletions.

The format is: Sheet 2
A/ B/
334702/ UEMR88QX
334703/ UEMR85QX
334704/ UEMR81QX
334707/ UEMR8JQX

The master worksheet has about 5000 items and the (A and B) data are both on it with other data ranging from (A-Y). My question is how do I have a cell look up data and return that it exists or doesn’t exist on the inventory sheet?

Master
A/ B/ C/ D/ E/
35/ 465/ 881676311350/ 311350/ UEMR8ZTU
36/ 469/ 881676310722/ 310722/ UEMR8V5V
37/ 483/ 881676310924/ 310924/ UEMR8XYU
38/ 805/ 881676331096/ 331096/ UEMR8J13

My other problem I need to take that months inventory list and have it look at the master list and return the system number from the master list (B) next to the matching inventory number (C). Allowing me to cross match inventory to master each month and save inventory worksheet each month.

I know I can copy the column and past is as a value so I won’t lose the numbers as the master changes but getting the data onto that months inventory has been a pain.