What is the vector of field F?

Question

SPECIFY THE COMPONENT function of a vector field F in R² with the following property.

F is everywhere normal to the line x=4

What are the possible vector field F?

1)f=(0,y)

2)f=(x,0)

3)f=(x,y)

4)f=(-y,x)

Answer 1

In order to be normal to the line x=4, each vector must be horizontal.

That means, its x-coordinate must be 0.

Only 1) satisfies that.