The correct answer is option 3, which states that the ratio of velocity of X-rays to that of gamma rays is 1.

To understand this, we need to know that electromagnetic waves, such as X-rays and gamma rays, all travel at the same speed in a vacuum, which is the speed of light. The speed of light is a fundamental constant, denoted by the symbol "c."

Therefore, regardless of their frequency or energy, X-rays and gamma rays both travel at the same velocity, which is the speed of light. This means that the ratio of their velocities is always 1.

It is important to note that the velocity of electromagnetic waves can change when they pass through a medium other than a vacuum, as their speed can be affected by the medium`s refractive index. However, in the context of the given question, where it refers to the velocity in a vacuum, the correct answer is option 3, meaning the ratio is 1.

Note: Alert - correct answer should be option 2, which states that the ratio of velocity of X-rays to that of gamma rays is greater than 1.