Correct Answer: MSSXN

Solution : Given:
S_NX_MNX_MN_SM_X

To fill the series we have to divide the series→S_NX/_MNX/_MN_/SM_X
Let's check each option –
First option: MSSXN; S M NX/ S MNX/ S MN X /SM N X (SMNX is repeated in the series.)
Second option: NXYMS; S N NX/ X MNX/ Y MN M /SM S X (No repeated pattern has been found.)
Third option: NMXXN; S N NX/ M MNX/ X MN X /SM N X (No repeated pattern has been found.)
Fourth option: SMNXX; S S NX/ M MNX/ N MN X /SM X X (No repeated pattern has been found.)

So, the series becomes→SMNXSMNXSMNXSMNX. Hence, the first option is correct.