Step 1: Sort by the four classes:
Indian instruments are grouped as tata (strings), sushira (wind), avanadha (skin drums) and ghana (solid percussion).
Step 2: Place each instrument:
Flute is sushira. Morsing is ghana. Tanpura, veena and violin are tata. Mridangam and khanjira are avanadha.
Step 3: Find the pair with both avanadha:
Only the pair in option 3 has two skin instruments. The other pairs have strings, wind or ghana instruments.
Final Answer:
Mridangam and Khanjira \[\boxed{3}\]