Ответ:

"mass media" is singular

Ответ:

"Media" is a collective noun, so it can be both plural and singular uncountable, depending on the situation.

In American English all collective nouns are treated like singular. Variations are possible in British English.

The mass media are reporting about the event. (newspapers, magazines, etc.)

/ The mass media is reporting about the event. (as a unity, or one entity)