Hydrogen atom will be in its ground state if its electron is in
A) any energy level
B) the lowest energy state
C) the highest energy state
D) the intermediate state

Hint: The electrons orbiting the hydrogen ion can only occupy discrete energy levels. The hydrogen atom will be in the ground state if the electron is in the ground state of energy.

Complete step by step answer:
We want to find the electron energy corresponding to the ground state of the hydrogen atom. The ground state of the hydrogen atom will correspond to the lowest energy state of the electron.
Since we measure the electron energy in terms of its potential energy which is negative by convention, the ground state of the electron corresponds to the lowest energy state of the atom. In this state, the electron will be as tightly bound to the nucleus as it can be. This also corresponds to the most negative potential energy of the electron which is why we say that it is the most strongly attracted to the nucleus in this state.
When a system has a strong negative potential energy, it is relatively stable compared to the excited states and hence it is called the ground state.

Hence option (B) is the correct choice.

Note: While the magnitude of the potential energy will be the highest in the ground state, its sign will be negative which is why we say it is the lowest numerically. The name ground state corresponds to the most stable state of the electron like how mechanical objects that are on the ground are the least likely to move due to gravity. However, for an electron, the lowest potential is not zero but the negative potential energy corresponding to the lowest energy state.