2u.3v=1(since unit vector)

 

implies 6u.v=1

 

implies 6 mod(u) mod(v) cos(theta)=1 (since angle between u and v is          

                                                              same as that of 2u and 3v)

 

implies 6 1 1 cos(theta)=1 (since u and v unit vectors)

 

implies cos(theta)= 1/6

 

so option B is correct.(since Theta belogs to either 1st or second quadrant)