Explanation:

- Census:

- A systematic and official enumeration of a population, conducted periodically.

- Usually includes details such as age, sex, and occupation.

- National Register of Citizens:

- A list of all the citizens in a particular area.

- Not regularly counted and focused on verifying citizenship.

- Demographic Count:

- Broad term that refers to the measurement of a population's characteristics.

- Not an official periodic enumeration.

- National Population Register:

- A government database with personal details of individuals residing in a country.

- Not specifically an enumeration but aims to serve administrative purposes.

Your understanding is spot on; Census is indeed the official periodic enumeration of a population. .