Question

Which element has two shells each one of which is completely filled with electrons?

• A. Na
• B. Al
• C. F
• D. Ne

Answer 1

The correct option is D

Ne

The outermost shell is the valence shell of the element. The elements in groups have similar electronic configuration of the valence shell.

Explanation for the correct option:

The shell with completely filled electrons mean the valence electrons are 8.

Number of valence electrons + 10 = Number of group

So, the element belong to group 18.

Number of shells = 2

Number of shells = Number of period

So, the element belong to period 2.

Therefore, the element that has two shells and completely filled electrons is Neon ($\mathrm{Ne}$).

Neon belongs to period 2 and group 18.

Explanation for the incorrect options:

Sodium ($\mathrm{Na}$) has three shells and it has one electron in valence shell.

Aluminium ($\mathrm{Al}$) has three shells and three electrons in valence shell.

Fluorine ($\mathrm{F}$) has two shells but have seven electrons in valence shell.

Final answer:

Hence, option (D) is the correct option.