Ans. 4

Lord Brahma has four heads. Vedas  are the Vani of Brahma, each Ved came from each mouth of  Brahma. the 4th ved Atharva was discovered later by Rishi Atharv  . At the end of each yuga Brahma undergoes in a state of meditation and from each mouth he preaches  vedas , once in the same state a Danav heard the 4th ved and he took the next birth as Rishi Atharv .

Name of four vedas :

1. RidVeda

2. SamaVeda

3. Yajurveda

4. Atharvaveda