Which is an acceptable set of quantum numbers for an electron?

An acceptable set of quantum numbers for an electron is  $2,1,-1,-\frac{1}{2}$

An expression used to quantify the energy levels at which atoms and molecules can exist is known as a quantum number. For the hydrogen atom's Schrödinger wave equation to have solutions, an electron in an atom or ion needs to have four quantum numbers to characterize its state.

Hence, option C is correct.