In electromagnetic waves travelling in vacuum
(i) The electric field $E$ is always perpendicular to the magnetic field $B$.
(ii) The cross product $\overrightarrow{E}\times \overrightarrow{B}$ always gives the direction in which the waves travel.
iii) The field $E$ and $B$ vary sinusoidally.
iv) There is a phase difference of $\frac{\pi }{2}$ between $E$ and $B$.
The correct statement(s) is (are)