Doubt from EM Waves

How to distinguish between option 2 and 3 ?

Intensity has a direct formula why he has done I/2 in this question?

After application of intensity formula, it is stated that half intensity is provided by electric field and other half by magnetic field. So I/2 is done..

So, if it is not mentioned in question then we will use the formula only, right?

Plz elaborate what is not mentioned in question.

Like in this one we will take whole intensity from Electric field only right

Yes because it is said maximum electric field.

Anyone please Try question in post 1

For post#1 you need to field direction of propagation vector and electric feild vector from given magnetic feild equation and then use E*B=C to get magnetic feild vetor.