The correct option is A 4
We know that if two vectors are orthogonal, their scalar product is zero.
So, we have
Let say →A=4^i−2^j−2^k and →B=−^i+2^j−m^k
Since, its scalar product will be zero
⇒ →A.→B=0
⇒ (4^i−2^j−2^k).(−^i+2^j−m^k)=0
⇒ −4−4+2m=0⇒ m=4