Which element has atoms with exactly four valence electrons in its ground state?

Silicon has atoms with exactly four valence electrons in its ground state.

Valence electrons are the number of electrons present in the outermost shell when the atomic number of an element is known. This is how the Aufbau principle should be applied when writing an electronic configuration. Like silicon, which contains four valence electrons because four of them are located in the outermost shell.

Hence, option C is correct.