The kinetic energy of an electron in the ground level of a hydrogen atom is K units.The values of its potential energy and total energy respectively are ________.

The correct option is -2K; -K.

To understand why this is correct, let us recall the relationship between kinetic energy, potential energy, and total energy for an electron in a hydrogen atom (or any Bohr orbit under an inverse-square electrostatic force).

According to Bohr's model of the hydrogen atom, the electrostatic force of attraction between the positively charged nucleus and the electron provides the necessary centripetal force for the circular orbit of the electron. From this, we can derive the expressions for kinetic energy ($K$), potential energy ($U$), and total energy ($E$).

For an electron in a stable orbit, the electrostatic potential energy is negative because of the attractive force between the opposite charges (the proton in the nucleus and the orbiting electron). The potential energy is given by:
$U=-2K$
where $K$ is the kinetic energy of the electron.

Given that the kinetic energy of the electron in the ground state is $K$ units, we have:
Kinetic Energy, $E_k=K$

Therefore, the potential energy ($U$) is:
$U=-2K$

The total energy ($E$) of the electron is the sum of its kinetic energy and potential energy:
$E=E_k+U$

Substituting the values of kinetic energy and potential energy into the equation:
$E=K+(-2K)$
$E=-K$

Thus, the values of potential energy and total energy are -2K and -K respectively.