A database is said to be in first normal form, or 1NF if it has a candidate key present.
A default relationaal Database or RDBMS is in 1NF. But, in the first normal form, level of redundancy is too high.
For a relational schema to be in 1NF, R must ensure that there are no multivalued attributes present. Which means, that all the attributes need to be atomicin the relation R.