Answer:
Oxygen has two vacancies in its electron shell, but carbon has four vacancies.
Step-by-step explanation:
Oxygen has vacant space for two electrons in its outermost shell. Hence, it can accommodate two electrons from two hydrogen atoms. This leads to the formation of the H₂O molecule. On the other hand, the Carbon atom has vacant space for four electrons. Hence, it can accommodate four electrons from four hydrogen atoms. This leads to the formation of the CH₄ molecule.
In this way the explanation can be provided by the following statement:
Oxygen has two vacancies in its electron shell, but carbon has four vacancies.