Use the wave relation

For an electromagnetic wave traveling in air (approximately same as vacuum), the speed is $c = 3 \times 10^8\ \text{m/s}.$

The relation between speed, frequency, and wavelength is $c = f\lambda.$

Given frequency

$f = 60\ \text{MHz} = 60 \times 10^6\ \text{Hz}.$

Calculate wavelength

$\lambda = \frac{c}{f} = \frac{3 \times 10^8}{60 \times 10^6}.$

Simplifying, $\lambda = \frac{3}{60} \times 10^2 = \frac{1}{20} \times 100 = 5\ \text{m}.$

About the field vectors

In an electromagnetic wave traveling along the $z$-direction, the electric field $\vec E$ and magnetic field $\vec B$ are both perpendicular to the direction of propagation and also perpendicular to each other.

Check options

• A: $2.5$ m
• B: $5$ m
• C: $10$ m
• D: $2$ m

Hence, the correct option is B.