Which one of the following is not related to the Rigvedic period?

Which one of the following is oldest Veda :

Which of the following Gods is referred to as 'Ritasya Gopa' in the Rigveda?

Which one of the following Brahmana texts belongs to the Rigveda?

Vedic river Askini is identified with which one of the following rivers?

Which of the following Rig-Vedic Gods is not mentioned in 'Boghazkoi' inscription?