If the speeds of gamma rays, X-rays and microwaves are $V_g, V_x$ and $V_m$, respectively in free space, then the correct relation between them is

$V_g = V_x = V_m$

The correct answer is Option (4) → $V_g = V_x = V_m$

All electromagnetic waves travel at the same speed in free space:

$V_g = V_x = V_m = c \approx 3 \times 10^8\ \text{m/s}$

∴ Correct relation: $V_g = V_x = V_m$