Four atoms of hydrogen combine with one carbon atom to form CH4, but only two hydrogen atoms combine with one oxygen atom to form H2O. Which of the following helps to explain why? Hydrogen has one valence electron.
Oxygen has two vacancies in its electron shell, but carbon has four vacancies.
Metallic bonds form between positively charged metal ions and delocalized electrons.
Atoms may share electrons in order to fill their electron shells.

Oxygen has two vacancies in its electron shell, but carbon has four vacancies.

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.

work: w = fd (given)

work done by chet   =50*1 = 50 j

work done by mika =40*2 = 80 j

work done by sara =30*1.5 = 45 j

work done by bill =60*0.5 = 30 j

students in order from the greatest amount of work done to the least is mika> chet> sara> bill

hence option (b) is correct.