In an electromagnetic wave,what has an average value of zero?

$A$ plane polarized monochromatic $EM$ wave is travelling in a vacuum along the $z$-direction such that at $t = t_1$,it is found that the electric field is zero at a spatial point $z_1$. The next zero that occurs in its neighborhood is at $z_2$. The frequency of the electromagnetic wave is:

The peak value of the magnetic field of an electromagnetic wave moving in a magnetic field is $20 \, nT$. The peak value of the electric field intensity is ..... $V/m$.

An electromagnetic wave of frequency $45 \text{ MHz}$ travels in free space along the $X$-axis. At some point and at some instant, the electric field has a maximum value of $750 \text{ NC}^{-1}$ along the $Y$-axis. The magnetic field at this position and time is

The $rms$ value of the electric field of the light coming from the sun is $720 \ N \ C^{-1}$. The average energy density of the electromagnetic wave is $...... \ J \ m^{-3}$.

$A$ plane electromagnetic wave of frequency $35 \ MHz$ travels in free space along the $X$-direction. At a particular point (in space and time) $\overrightarrow{E} = 9.6 \ \hat{j} \ V/m$. The value of the magnetic field at this point is: