Bibliometry is

The correct answer is C. Bibliometrics is an information management tool: it applies statistical and mathematical methods to books, journal articles and other written records to study patterns of publication, citation, authorship and use.

• A (Function of Library Network): Wrong. Library networks such as INFLIBNET and DELNET are cooperative arrangements for sharing resources. They are organisations, not methods of analysis.
• B (Information Management service): Tempting, but wrong. Services are what libraries deliver to users, such as reference, circulation or current awareness. Bibliometrics is the analytical method used to understand and manage the literature.
• D (Library Service): Wrong for the same reason. It describes direct patron-facing work, not a measurement technique.

The core concept is the set of bibliometric laws and indicators: Lotka's law of author productivity, Bradford's law of journal scatter, Zipf's law of word frequency, the impact factor and the h-index. Librarians use these to decide acquisitions and weed collections. In Mains, the same ideas feed into research evaluation, institutional ranking and the debate on open access.

Trap: Aspirants pick B because "information management" sounds like the broad field. The question treats bibliometrics as a tool, a method of measurement, not a service.