Which element has twice as many electrons in its second shell as in the first shell?

The correct option is C

$\mathrm{C}$

Explanation for the correct option:

The given element contains 2 electrons in the first shell and 4 electrons in the outermost shell.

Number of valence electrons in the valence shell = 4

Number of valence electrons + 10= Number of group

So, the element belong to group 14.

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 four valence electrons is Carbon ($\mathrm{C}$).

Carbon belongs to period 2 and group 14.

Explanation for the incorrect option:

Beryllium ($\mathrm{Be}$) has two electrons in first shell and two electrons in second shell.

Boron ($\mathrm{B}$) has two electrons in first shell and three electrons in second shell.

Nitrogen ($\mathrm{N}$) has two electrons in first shell and five electrons in second shell.

Final answer:

Hence, option (C) is the correct option.