CBSE Class 11-science Answered

given vector product  is  

we re given that q = 1

hence ,

where θ is the angle between and

From above expression, we see that magnitude of can be calculated only if we know the

angle between and but we are not given that angle .

Hence we check the given options of magnetic field so that we need to get dot product of

and is zero because these vectors are perpendicular to each other

If then 

if then

if we do similar dot product calculation, we see that other options are not satisfying the above condition.

Hence the correct vector is