The correct option is D →b and →c are mutually perpendicular.
We have,
→a=17(3^i+2^j+6^k)
→b=17(3^i−6^j+2^k)
→c=17(6^i+2^j−3^k)
Then,
→a.→b=17(3^i+2^j+6^k).17(3^i−6^j+2^k)
=149(9−12+12)≠0
Similarly finding, →b.→c
→b.→c=0
∴→b,→c are mutually perpendicular.