#### Assertion: The energy of a photon is directly proportional to its frequency.Reasoning: According to Planck's quantum theory, the energy of a photon is given by the equation $E=hf$,where h is Planck'sconstant and f is the frequency of the photon.Option: 1 Both Assertion and Reasoning are true, and Reasoning is the correct explanation of the Assertion.  Option: 2 Both Assertion and Reasoning are true, but Reasoning is not the correct explanation of the Assertion.Option: 3  Assertion is true, but Reasoning is false.  Option: 4 Assertion is false, but Reasoning is true.

The energy of a photon is directly proportional to its frequency. This is based on Planck's quantum theory, which states that the energy of a photon is given by the equation $E=hf$ , where h is Planck's constant and f is the frequency of the photon. This means that as the frequency of a photon increases, its energy also increases proportionally. Therefore, Assertion is true. Reasoning correctly explains why the Assertion is true.