Correct Answer: avrakdv

Solution : Given:
_ad_vk_a_dvv_raa_v_kr

To fill the series, we have to divide the series – _ad_vk_ / a_dvv_r / aa_v_kr
Let's check each option –
First option: avrkadv; a ad v vk r / ak k dvv a r / aa d v v kr (No repeated pattern found.)
Second option: avrakdv; a ad v vk r / a a dvv k r / aa d v v kr (aadvvkr is repeated in the series.)
Third Option: varvkdv; v ad a vk r / a v dvv k r / aa d v v kr (No repeated pattern found.)
Fourth option: avrvada; a ad v vk r / a v dvv a r / aa d v a kr (No repeated pattern found.)

So, the series becomes→aadvvkraadvvkraadvvkr. Hence, the second option is correct.