In an electromagnetic wave, the ratio of energy densities of electric and magnetic fields is ___________.

Correct option is A

​$$\text{The respective energies due to electric and magnetic field is given by,}\\u_E = \frac{1}{4} \epsilon_0 E_0^2\\u_B = \left( \frac{1}{4} \right) \frac{B_0^2}{\mu_0}\\\text{So, taking ratio, } u_E : u_B = 1 : 1$$​​