Assertion: Penetrating power of X−rays increases with the increasing wavelength.
Reason: The penetrating power of X−rays increases with the frequency of X-rays.
A. If both assertion and reason are true and the reason is the correct explanation of the assertion.
B. If both assertion and reason are true but reason is not the correct explanation of the assertion.
C. If the assertion is true but the reason is false.
D. If the assertion and reason both are false
E. If the assertion is false but the reason is true.

Hint: When it comes to big particles, heavier and more charged particles penetrate less deeply than lighter and less charged ones. For massless particles, the penetrating power of the rays depends directly on their frequency; the higher the frequency, the greater the penetrating power.

Complete step by step solution:
Hard X-rays are X-rays with short wavelengths and strong penetrating power that are extremely destructive. Particle radiations have a non-zero net energy even when they are at rest because their constituent particles have masses. The overall energy of particle radiation is influenced by the constituent particle's speed, which can naturally vary.

Particle radiation penetrating capability is mostly influenced by its charge and mass rather than its energy. Due to head-on collisions, radiation with a higher mass can be easily halted by the atoms of barriers. Additionally, when charged, the particle interacts electrostatically with the barrier's atoms, which reduces the power of the penetration.

As wavelength is inversely proportional to penetration power and the frequency of the X-rays. Therefore, we can say that if we increase the wavelength then the penetration power of X-rays is reduced and if we increase the frequency of X-rays then its penetration power increases. Soft X-rays are X rays used for medical procedures because they are less invasive and have longer wavelengths.

Hence option E is correct.

Note: These highly invasive radiations are regarded as being extremely harmful. Externally, the radiation is deemed to be more hazardous the higher the penetrating power. For instance, beta particles can pass through skin but alpha rays cannot. However, internally (such as when inhaled or eaten), alpha rays may cause more tissue damage than beta particles because of their bigger masses and intense radiation.