1. A photon with an energy of 13 .6 eV knocks out an electron from a hydrogen atom at rest, which is in the ground state. The kinetic energy of an electron away from the nucleus is (eV) 5) 13,6 1) -13,6 2) 10,2 3) 3,4 4) 0

The correct answer is 1) $-13,6$.<br /><br />When a photon with an energy of 13.6 eV knocks out an electron from a hydrogen atom at rest, the electron is ejected from the atom with a kinetic energy equal to the energy of the photon, but in the opposite direction. This is because the photon transfers all of its energy to the electron, causing it to be ejected from the atom.<br /><br />Since the electron is moving away from the nucleus, its kinetic energy is negative. This is because the electron is moving in the opposite direction to the direction of the photon's momentum, which is defined as positive. Therefore, the kinetic energy of the electron is $-13,6$ eV.